LIBRARY  OF  THE 
UNIVERSITY  OF  ILLINOIS 
AT  URBANA-CHAMPAIGN 


5  81  . 1 5 

C59ph 
coo  .2 


Agr i c . 


The  person  charging  this  material  is  re¬ 
sponsible  for  its  return  on  or  before  the 
Latest  Date  stamped  below. 

Theft,  mutilation,  and  underlining  of  books 
are  reasons  for  disciplinary  action  and  may 
result  in  dismissal  from  the  University. 


THE  PHYTOMETER  METHOD  IN  ECOLOGY 

THE  PLANT  AND  COMMUNITY  AS  INSTRUMENTS 


Frederic  E.  Clements  and  Glenn  W.  Goldsmith 


\ 


Published  by  the  Carnegie  Institution  of  Washington 

Washington,  December  1924 


i 


N.  Y.  STATE  COUBrf  cT*t*iCUi.TWK 
U/KNEU.  UNIVERSITY,  iihALA,  K.  Y 


CLEMENTS  AND  GOLDSMITH 


PLATE  1 


O 

LO 

ii 


< 


o 

o 

00 

o 


UJ 

o 

Z) 

H 


LO 

CO 

LO 

(\j 

CO 


o 

CO 

OJ 


LO 

CD 


LO 


O 

O 

LO 


Ld 

Q 

=) 

H 

(- 


O 

O 

m 

(Vl 


Ld 

D 

D 

h 

l~ 

_J 

< 


oj 

oJ 

CD 


<D 

9,  <o 

OJ  U 

LO  ^ 
LO  CD 


O 

C\J 


b- 

CD 

ob 


CO 

cb 

CD 


</ 


UJ 


CO 

UJ 


cO 


Ld 


-OJ 


Ld 


-CJ 


V 


CO 

21 

< 

_I 

CL 


< 

H 

CO 


ud 

11 


o  o 

=5  jZ 

£  < 

0-  |— 

CO 


I- 


0O 


U0 


CO 


Ld 


Qb 

Id 

CD 


I— 


1 — 
CO 


UJ 

_1 

Q 

O 

< 

CO 


\— 

< 

f— 

cO 


Transect  through  phytometer  stations  from  plains  grassland  at  Colorado  Springs  to  alpine  meadow,  Pike  s  Peak. 


THE  PHYTOMETER  METHOD  IN  ECOLOGY 

THE  PLANT  AND  COMMUNITY  AS  INSTRUMENTS 


BY 

Frederic  E.  Clements  and  Glenn  W.  Goldsmith 


Published  by  the  Carnegie  Institution  of  Washington 

Washington,  December  1924 


Judd  &  Detweiler,  Inc. 
Washington,  D.  C. 


ffl.js 

(LSf 


UNIVERSITY  OF  ILLINOIS 
AGRICULTURE  LIBRARY 

CONTENTS. 


4 

€  <  .-iMc 


Page 


List  of  illustrations .  v 

Scope  and  essentials .  3 

Nature  of  quantitative  ecology .  3 

Advantages  of  instruments .  4 

Disadvantages  of  instruments .  4 

Plant’s  relation  to  factors .  4 

Possibility  of  using  plants  as  measures .  5 

Preliminary  uses  of  plants .  6 

Kinds  of  phytometers . 9 

Control  phytometers .  9 

Transplant  phytometers .  10 

Indicator  phytometers .  10 

Responses  measured .  11 

Nature  and  role  of  zoometers .  12 

Essentials  of  the  phytometer  method . 12 

Climaxes  and  climates  of  the  Pike’s  Peak  region .  14 

Mixed  prairie . .  14 

Montane  forest .  15 

Subalpine  forest .  16 

Alpine  meadow .  16 

Methods  and  results,  season  of  1918 .  17 

Temperature .  19 

Humidity  and  evaporation .  20 

Summary .  20 

Phytometers,  first  series .  21 

Readings .  21 

Phytometers,  second  series .  22 

Readings... .  22 

Phytometers,  third  series .  23 

Readings . . 23 

Summary .  23 

Methods  and  results,  season  of  1919 . 25 

Temperature .  25 

Humidity  and  evaporation .  26 

Summary . 26 

Phytometers,  first  series .  27 

Readings .  28 

Phytometers,  second  series .  29 

Readings .  30 

Summary . 30 

Methods  and  results,  season  of  1920 .  31 

Temperature .  32 

Holard  and  humidity .  33 

Evaporation .  34 

Wind .  34 

Summary .  34 

Phytometers,  first  series .  35 

Transpiration .  37 

Growth .  41 

Dry  weight .  41 

Water  requirement .  43 

Summary .  43 

Second  series .  44 

Transpiration .  44 

Growth .  47 

Dry  weight  and  water  requirement .  49 

Summary . 50 


in 


IV 


CONTENTS. 


Methods  and  results,  season  of  1920 — Continued  Page 

Large  phytometers .  51 

General  summary,  1918-1920 .  53 

Methods  and  results,  season  of  1923 .  55 

First  series .  55 

Containers .  56 

Temperatures .  57 

Humidity  and  evaporation .  58 

Light .  59 

Transpiration .  60 

Growth . 60 

Dry  weight  and  water  requirement .  61 

Soil-air .  61 

Second  series .  62 

Stations  and  installation .  62 

Temperature .  63 

Humidity  and  evaporation .  63 

Light . . .  64 

Transpiration .  65 

Growth .  65 

Dry  weight  and  water  requirement .  66 

Short-period  phytometers .  67 

Applications .  68 

Methods .  68 

Installation  for  1923 .  70 

Sun  and  shade .  71 

Surface,  slope,  exposure,  and  altitude .  73 

Related  applications  of  the  phytometer  method .  74 

Slope-exposure  studies .  74 

Installation .  75 

Summary .  77 

Transpiration  and  growth  in  the  grassland  climax .  78 

Phytometer  batteries .  78 

Community  phytometers .  81 

Sod-core  phytometers .  81 

Methods .  82 

Results .  83 

Field-plot  phytometers . 84 

Cut-quadrat  phytometers .  84 

Results  at  grassland  stations .  86 

Results  in  grazing  exclosures .  86 

Transplant  phytometers .  88 

Species  phytometers . 88 

Community  phytometers .  88 

R6sum6 .  89 

Values  and  limitations  of  the  phytometer  method .  89 

Tables .  90 

Bibliography . 105 


LIST  OF  ILLUSTRATIONS. 

PLATES. 


Plate  1.  Transect  through  phytometer  stations  from  plains  grassland  at  Colorado 
Springs  to  alpine  meadow,  Pike’s  Peak.  Frontispiece. 

Plate  2. 

A.  Mixed  prairie  at  the  plains  station,  6,100  feet,  Colorado  Springs. 

B.  Montane  forest  ( Pseudotsuga  mucronata )  at  the  montane  station,  8,600  feet,  Al¬ 

pine  Laboratory. 

Plate  3. 

A.  Subalpine  forest  ( Picea  engelmanni )  at  the  subalpine  station,  10,800  feet,  Pike’s 

Peak. 

B.  Battery  of  large  wheat  phytometers,  montane  station,  1920. 

Plate  4. 

A.  Battery  of  sunflower  phytometers,  plains  station,  1918. 

B.  Battery  of  sunflower  phytometers,  montane  station,  1918. 

C.  Battery  of  oat  and  wheat  phytometers,  montane  station,  1918. 

Plate  5. 

A.  Sun  station,  1923. 

B.  Half-shade  station,  1923. 

Plate  6. 

A.  Full-shade  station,  1923. 

B.  Photosynthesis  and  respiration  phytometers,  sun  station,  1923. 

Plate  7. 

A.  Sunflower  phytometers,  sun  station,  first  series,  1923. 

B.  Same,  half-shade  station. 

C.  Same,  full-shade  station. 

Plate  8. 

A.  Growth  of  shoots,  shade,  half-shade,  and  sun  stations,  second  series,  1923. 

B.  Growth  of  roots,  sun,  half-shade,  and  shade  stations. 

Plate  9. 

A.  Battery  of  sunflower  phytometers,  slope-exposure  transect,  mesocline  station. 

B.  Same,  canyon-bottom  station. 

C.  Same,  xerocline  station. 

Plate  10. 

A.  Sod-core  phytometers  and  details  of  installation,  Burlington,  Colorado. 

B.  Clip-quadrat  phytometer  in  Bulbilis-Bouteloua  short-grass,  Burlington. 

Plate  11. 

A.  Agropyrum  glaucum  from  clip-quadrats  in  cattle-prairie  dog  enclosure,  cattle  ex¬ 

closure,  and  open  range,  Grand  Canyon,  Arizona. 

B.  Cattle-rodent  exclosure,  Santa  Rita  Range  Reserve,  Tucson,  Arizona,  showing 

growth  of  desert  plains  grassland  under  complete  protection. 


TEXT-FIGURES. 

Page 


1.  Average  temperature  (heavy  lines)  and  humidity  (light  lines),  1918 .  17 

2.  Average  standard  evaporation,  1918 .  20 

3.  Average  temperature  for  day  (heavy  lines),  24-hours  (medium  lines),  and  night 

(light  lines),  1919 .  26 

4.  Average  humidity  for  day  (heavy  lines),  24-hours  (medium  lines),  and  night  (light 

lines),  1919 .  27 

5.  Average  evaporation,  1919 .  28 

6.  Average  temperature  for  day  (heavy  lines),  24  hours  (medium  lines),  and  night 

(light  lines),  1920  .  31 

7.  Average  rainfall,  24-hour  humidity,  total  wind,  and  average  evaporation,  1920.  ...  32 

8.  Average  leaf-area  and  transpiration  of  sunflowers,  first  series,  1920  .  36 

9.  Average  stem  length  and  diameter  of  sunflowers,  first  series,  1920 .  37 


v 


VI 


LIST  OF  ILLUSTRATIONS 


TEXT  FIGURES — Continued. 

Page 

10.  Average  leaf-area  and  transpiration  of  wheat,  first  series,  1920 .  38 

11.  Average  leaf-area  and  transpiration  of  oats,  first  series,  1920 .  39 

12.  Average  transpiration  of  sunflowers  and  physical  factors,  first  series,  1920;  plains 

(below),  montane  (mid),  subalpine  (above) .  40 

13.  Average  transpiration  of  wheat,  and  physical  factors,  first  series,  1920:  plains 

(below),  montane  (mid),  subalpine  (above) .  40 

14.  Average  transpiration  of  oats,  and  physical  factors:  plains  (below),  montane 

(mid),  subalpine  (above) .  42 

15.  Average  leaf-area  and  transpiration  of  sunflowers,  second  series,  1920 .  42 

16.  Average  stem  length  and  diameter  of  sunflowers,  second  series,  1920 .  45 

17.  Average  leaf-area  and  transpiration  of  wheat,  second  series,  1920 .  46 

18.  Average  leaf-area  and  transpiration  of  oats,  second  series,  1920 .  47 

19.  Average  transpiration  of  sunflowers,  and  physical  factors,  second  series,  1920  .  48 

20.  Average  transpiration  of  wheat,  and  physical  factors,  second  series,  1920  .  48 

21.  Average  transpiration  of  oats,  and  physical  factors,  second  series,  1920 .  50 

22.  Average  transpiration  of  large  phytometers  and  wheat,  first  series,  1920 .  52 

23.  Average  transpiration  of  large  phytometers,  1920,  compared  with  factor  data .  53 

24.  Water  requirements  of  plants  of  first  and  second  series  1920 . . .  54 

25.  Average  temperature  for  day  (heavy  lines),  24-hours  (medium  lines),  and  night 

(light  lines),  1923 .  56 

26.  Average  24-hour  temperature  (heavy  line),  average  daily  wind  (medium  line),  and 

average  standard  evaporation  (light  line),  1923.  Each  space  equals  5  units; 
the  base-line  is  0  for  evaporation  and  wind  and  25  for  temperature .  57 

27.  Average  transpiration  of  sunflowers,  1923 . . .  58 

28.  Average  transpiration  of  sunflowers,  sun  station,  1923,  compared  with  fad  or  data. 

Each  space  equals  5  units  except  for  the  inverted  humidity  curve,  for  which 
the  value  is  10;  the  base-line  is  0  for  transpiration,  wind,  and  evaporation,  and 
25  for  temperature .  59 

29.  Average  transpiration  of  sunflowers,  half-shade  station,  1923,  compared  with  factor 

data;  values  as  in  fig.  28 .  60 

30.  Average  transpiration  of  sunflowers,  shade  station,  1923,  compared  with  factor  data; 

values  as  in  fig.  28 .  61 

31.  Average  leaf-area  of  sunflowers,  first  series,  1923 .  63 

32.  Average  stem-length  of  sunflowers,  first  series,  1923 .  64 

33.  Average  stem-width  of  sunflowers,  first  series,  1923 .  65 

34.  Average  leaf-area  of  sunflowers,  second  series,  1923  . 66 

35.  Average  stem-length  of  sunflowers,  second  series,  1923  .  67 

38.  Average  stem-width  of  sunflowers,  second  series,  1923 .  69 

37.  Light  intensity  in  terms  of  meridian  sun,  August  26,  1923 . .  .  70 

38.  Average  transpiration  per  leaf  product  (light  lines),  and  average  evaporation 

(heavy  lines);  short-period  phytometers,  September  18,  1923 .  71 

39.  Average  transpiration  per  leaf  product  (light  lines),  and  average  evaporation  (heavy 

lines);  short-period  phytometers,  September  20,  1923 .  71 

40.  Average  transpiration  per  leaf  product  (light  lines),  and  average  evaporation 

(heavy  lines);  short-period  phytometers,  September  26-27,  1923 .  72 

41.  Comparison  of  air  and  soil  temperatures  on  north  (light  lines)  and  south  (heavy 

lines)  slope-exposures,  Alpine  Laboratory .  74 

42.  Monthly  value  for  wind,  evaporation,  and  light  in  slope-exposure  transect .  75 

43.  Comparison  of  holard  percentages  in  slope-exposure  transect;  south  slope- 

exposure  (heavy  lines),  north  (medium  lines),  bottom  of  canyon  (light  lines) .  .  76 

44.  Average  dry  weight  and  transpiration  of  phytometers  in  slope-exposure  transect; 

south  slope-exposure  (heavy  lines),  north  (medium  lines),  bottom  of  canyon 
(light  lines) .  78 

45.  Comparative  growth  and  dry  weight  of  phytometers  in  slope-exposure  transect ....  79 


THE  PHYTOMETER  METHOD  IN  ECOLOGY. 
THE  PLANT  AND  COMMUNITY  AS  INSTRUMENTS 

By 

Frederic  E.  Clements  and  Glenn  W.  Goldsmith 


THE  PHYTOMETER  METHOD  IN  ECOLOGY. 


SCOPE  AND  ESSENTIALS. 

NATURE  OF  QUANTITATIVE  ECOLOGY. 

The  first  attempt  to  organize  ecological  research  upon  a  quantitative 
basis  was  made  in  “Research  Methods  in  Ecology”  nearly  20  years  ago. 
While  this  has  met  with  much  success,  it  is  not  yet  generally  recognized 
that  the  term  ecology  connotes  a  study  of  the  relation  between  organism 
and  habitat,  which  demands  the  use  of  exact  methods.  For  this  reason  it 
appears  fortunate  that  the  floristic  study  of  vegetation,  so  much  in  vogue 
on  the  continent  of  Europe,  is  rapidly  coming  to  be  known  as  plant 
sociology.  To  the  ecologist,  however,  the  cause-and-effect  relation  between 
plant  and  habitat  is  more  than  ever  “the  central  and  vital  part  of  botany,” 
in  the  investigation  of  which  quantitative  methods  alone  can  yield  results 
of  fundamental  and  permanent  value.  The  emphasis  given  to  this  as  a 
guiding  principle  in  “Research  Methods”  may  be  recalled  with  profit  at 
the  present  time. 

“In  seeking  to  lay  the  foundation  for  a  broad  and  thorough  system  of 
ecological  research,  it  is  necessary  to  scan  the  whole  field  and  to  discrimi¬ 
nate  carefully  between  what  is  fundamental  and  what  is  merely  collateral. 
The  chief  task  is  to  discover,  if  possible,  such  a  guiding  principle  as  will 
furnish  a  basis  for  a  permanent  and  logical  superstructure.  In  ecology,  the 
one  relation  that  is  precedent  to  all  others  is  the  one  that  exists  between  the 
habitat  and  the  plant.  This  relation  has  long  been  known,  but  its  full  value 
is  yet  to  be  appreciated.  It  is  precisely  the  relation  that  exists  between 
cause  and  effect,  and  its  fundamental  importance  lies  in  the  fact  that  all 
questions  concerning  the  plant  lead  back  to  it  ultimately.  Other  relations 
are  important,  but  no  other  is  paramount,  or  able  to  serve  as  the  basis  of 
ecology.  Ecology  sums  up  this  relation  of  cause  and  effect  in  a  single  word, 
and  it  may  be  that  this  advantage  will  finally  lead  to  its  general  acceptance 
as  the  proper  name  for  this  great  field. 

“Any  serious  endeavor  to  find  in  the  habitat  those  causes  which  are  pro¬ 
ducing  modification  in  the  plant  and  in  vegetation  can  not  stop  with  the 
factors  merely.  The  next  step  is  to  determine  the  quantity  of  each.  It  is 
not  sufficient  to  hazard  a  guess  at  this,  or  to  make  a  rough  estimate  of  it. 
Habitats  differ  in  all  degrees  and  it  is  impossible  to  institute  comparisons 
between  them  without  an  exact  measure  of  each  factor.  It  is  of  little  value 
to  know  the  general  effect  of  a  factor,  unless  it  is  known  to  what  degree  this 
effect  is  exerted.  For  this  purpose  it  becomes  necessary  to  appeal  to  instru¬ 
ments,  in  order  to  determine  the  exact  amount  of  each  factor  that  is  present 
in  a  particular  habitat,  and  hence  to  determine  the  ratio  between  the 
stimulus  and  the  amount  of  structural  adjustment  that  results.  The 
employment  of  instruments  of  precision  is  clearly  indispensable  for  the 
task  which  we  have  set  for  ecology,  and  every  student  that  intends  to  strike 
at  the  roots  of  the  subject  and  to  make  lasting  contributions  to  it,  must 
familiarize  himself  with  instrumental  methods.” 


3 


4 


THE  PHYTOMETER  METHOD. 


ADVANTAGES  OF  INSTRUMENTS. 

The  improvement  of  meteorological  instruments  made  it  possible  to  begin 
the  measurement  of  habitats  with  a  considerable  equipment  and  to  devise 
new  or  modified  types.  The  chief  lack  was  with  respect  to  instruments  for 
determining  water-content  and  light,  the  two  most  important  factors  to 
the  plant.  This  was  met  by  the  development  of  a  series  of  photometers, 
as  well  as  various  kinds  of  geotomes  and  soil-borers.  However,  these  were 
less  available  than  the  standardized  meteorological  instruments,  which  came 
to  constitute  the  usual  equipment  for  factor  studies,  with  the  addition  of  the 
porous-cup  atmometer.  These  had  the  further  advantage  of  being  more  or 
less  familiar  and  their  readings  were  expressed  in  terms  readily  under¬ 
standable,  and  they  also  made  it  possible  to  compare  the  observations  taken 
in  a  particular  habitat  with  the  records  of  the  same  factors  accumulated 
by  weather  bureaus,  and  thus  to  broaden  the  scope  of  the  investigation. 
The  development  of  recording  instruments  for  temperature,  humidity,  light, 
wind,  etc.,  greatly  increased  the  effective  range  of  the  worker  and  con¬ 
served  both  his  time  and  energy.  Finally,  the  complete  battery  of  physical 
instruments  came  to  have  a  new  value  in  interpreting  the  results  obtained 
from  phytometers  and  often  by  converting  them  into  more  intelligible  terms. 

DISADVANTAGES  OF  INSTRUMENTS. 

A  fundamental  and  inevitable  drawback  to  all  instruments  is  the  failure 
to  express  factor  differences  in  terms  of  the  plant.  The  objection  has  often 
been  made  that  it  is  possible  to  measure  all  the  major  factors  of  a  habitat 
without  an  adequate  return  in  determining  the  behavior  of  the  plants  them¬ 
selves.  While  this  is  partly  due  to  the  lack  of  quantitative  studies  of 
functions  under  field  conditions,  it  arises  chiefly  from  our  present  inability 
to  express  physiological  activity  in  terms  of  physical  factors,  a  condition 
that  the  phytometer  method  is  designed  to  remedy.  A  further  disadvantage 
lies  in  the  fact  that  accuracy  is  greatest  with  the  instruments  that  measure 
the  less  important  indirect  factors,  such  as  temperature,  wind,  and  pressure, 
and  least  with  those  for  determining  the  direct  factors,  humidity,  water- 
content,  and  light.  Moreover,  the  recording  instruments  are  in  general  less 
accurate  than  the  simple  ones,  and  their  increased  cost  in  recent  years  has 
practically  put  them  out  of  the  reach  of  the  individual  investigator. 
Existing  recorders  need  to  be  simplified  in  some  cases  and  new  instruments 
should  be  devised  in  others,  with  especial  consideration  of  the  fact  that  the 
cost  of  a  complete  battery  of  ecological  instruments  has  greatly  retarded 
adoption  of  quantitative  methods  in  ecology;  even  more  critical  is  the 
failure  of  most  instruments  to  integrate  the  factors  concerned,  since 
measurements  of  function  are  regularly  obtained  as  sums.  It  is  this  con¬ 
sideration,  coupled  with  the  plant’s  judgment  as  to  efficient  factors,  that 
makes  the  phytometer  indispensable  to  quantitative  ecology. 

PLANT’S  RELATION  TO  FACTORS. 

The  distinction  between  direct  and  indirect  factors  is  prerequisite  to  a 
proper  understanding  of  the  relations  of  plant  and  habitat  (Clements,  1907). 
A  direct  factor  is  one  that  produces  an  immediate  response  in  function,  such 


SCOPE  AND  ESSENTIALS. 


5 


as  water,  light,  or  oxygen,  while  an  indirect  one  affects  the  plant  only 
through  some  direct  factor.  In  short,  the  measurement  of  direct  factors 
furnishes  the  clue  to  the  behavior  of  plant  or  community,  while  that  of 
indirect  factors  helps  to  explain  the  amounts  of  direct  ones  present.  In  the 
majority  of  habitats  the  determination  of  water- content,  humidity,  and 
light  suffices  for  a  fairly  complete  understanding  of  plant  behavior,  and 
the  measurement  of  indirect  factors  is  important  chiefly  in  the  comparative 
study  of  habitats.  Moreover,  the  decision  as  to  the  amount  or  intensity  of 
any  factor  necessary  to  produce  a  change  in  function  or  structure  can  be 
rendered  only  by  the  plant.  The  sensibility  of  instruments  is  often  greater 
than  that  of  the  plant,  and  this  sometimes  gives  a  fictitious  significance  to 
the  results.  The  efficiency  of  a  direct  factor  can  be  determined  only  by  the 
response  made  by  the  plant  or  group,  and  hence  it  will  necessarily  vary 
with  the  plants  concerned.  On  the  other  hand,  the  effectiveness  of  indirect 
factors  is  measured  by  the  consequent  modification  of  direct  ones,  and  not 
by  an  immediate  action  upon  the  plant.  Thus,  while  the  factors  of  a 
habitat  may  be  readily  ascertained  by  means  of  instruments,  their  signifi¬ 
cance  in  the  development  or  structure  of  the  plant  or  community  must  be 
determined  by  the  latter.  In  this  lies  the  essence  of  the  phytometer  method. 
Effects  must  be  determined  by  the  plant,  and  the  factor  intensities  that 
produce  them  must  be  measured  by  instruments. 

POSSIBILITY  OF  USING  PLANTS  AS  MEASURES. 

In  a  general  way,  plants  serve  as  measures  of  conditions  wherever  they 
grow.  This  is  the  principle  that  underlies  the  indicator  value  of  native 
plants.®  It  operates  with  equal  force  in  the  case  of  cultivated  plants  and 
crops  of  all  sorts,  though  with  these  it  must  be  recognized  that  the  habitat 
has  been  artificially  modified  to  some  degree.  Whenever  a  species  is 
planted  under  new  conditions  of  soil  or  climate,  it  serves  as  a  kind  of 
practical  phytometer  by  comparison  with  its  usual  growth.  To  give  this 
definite  value  it  is  necessary  to  measure  its  response  along  with  the  con¬ 
ditions  that  control  it.  This  has  led  to  the  use  of  standard  plants,  selected 
from  species  that  grow  vigorously  under  control  and  offer  few  difficulties 
in  handling  and  measuring.  At  present  certain  cultivated  plants  constitute 
the  best  biological  instruments,  but  it  is  possible  that  some  native  species 
will  prove  less  variable.  In  addition  to  this  use,  it  is  to  be  expected  that 
cultivated  plants  will  be  most  successful  as  phytometers  for  cropping  con¬ 
ditions  and  native  ones  for  the  natural  habitats  with  which  forestry  and 
grazing  are  concerned. 

In  the  first  attempts  to  develop  a  method,  leafy  shoots  were  employed  in 
potometers  with  considerable  success.  With  the  growing  recognition  of 
the  sharp  limitations  of  potometers,  this  practice  has  been  discontinued, 
though  under  proper  checks  and  for  short  periods  it  still  has  a  certain  value. 
The  paramount  consideration  in  using  phytometers  is  that  each  battery 
should  exhibit  the  actual  effect  of  the  habitat  and  not  mask  this  by  the 
variability  of  the  individuals.  This  difficulty  has  been  met  in  various  ways, 


“Carnegie  Inst.  Wash.  Pub.  No.  290,  1920. 


6 


THE  PHYTOMETER  METHOD. 


as  indicated  later.  It  is  eliminated  to  a  large  degree  when  the  number  of 
plants  is  large,  as  in  a  crop  plot  or  a  transplanted  quadrat, 

PRELIMINARY  USES  OF  PLANTS. 

While  the  intentional  use  of  plants  as  instruments  for  measuring  factors 
dates  from  1906,  the  essence  of  the  method  is  to  be  found  not  only  in  all 
experimental  planting,  but  also  in  the  comparative  study  of  growth  and 
function  under  different  conditions  by  means  of  pot  cultures.  This  is 
especially  true  of  the  chresard-echard  investigations  from  the  early  studies 
of  Sachs  (1859,  1865),  Heinrich  (1874),  and  Mayer  (1875)  to  those  of 
Gain  (1895),  Clements  (1900,  1904),  Hedgcock  (1902),  Briggs  and  Shantz 
(1912),  and  Crump  (1913).  The  method  was  actually  initiated  when 
plants  were  put  in  different  conditions  in  the  field,  though  in  most  of  this 
work  attention  was  directed  to  the  plants  as  affected  by  the  factors  rather 
than  as  measures  of  them.  The  next  step  in  advance  was  to  employ  plants 
as  instruments  in  measuring  the  effects  of  different  habitats,  and  the 
present  stage  is  represented  by  the  series  of  investigations  designed  pri¬ 
marily  to  develop  the  phytometer  method  into  an  indispensable  tool  for 
the  quantitative  ecologist. 

The  earliest  example  of  the  first  step  was  afforded  by  the  classic  experi¬ 
ments  of  Bonnier  (1890),  in  which  he  made  reciprocal  plantings  of  alpine 
and  lowland  plants.  This  was  the  first  important  application  of  the 
transplant  method,  which  has  been  developed  into  one  of  the  most  signifi¬ 
cant  uses  of  the  phytometer,  but  it  led  to  no  further  advance,  probably 
because  Bonnier’s  interest  in  factors  was  secondary  and  did  not  result  in 
the  measurement  of  them.  Clements  (1904  :  26;  1905  :  33,  115)  employed 
plants  to  determine  the  chresard  of  different  soils  in  the  field,  under  mea¬ 
sured  conditions  of  the  various  direct  factors.  Hesselmann  (1904  :  413,  379) 
made  use  of  potometers  and  potted  plants  of  several  native  species  to 
determine  the  transpiration  in  sun  and  shade,  in  addition  to  the  use  of 
leaves  for  ascertaining  the  relative  photosynthesis  and  respiration.  Sun  and 
shade  forms  of  various  polydemic  species  were  isolated  in  soil  blocks,  and 
the  water-loss  determined  by  weighing  on  the  spot.  He  also  studied  the 
structural  response  of  the  leaves  to  sun  and  shade,  and  this  phase  of  the 
problem  was  carried  much  further  by  the  extensive  investigations  of  E. 
Clements  (1905)  on  the  behavior  of  ecads  under  measured  conditions  in  the 
Rocky  Mountains.  The  first  use  of  plants  for  the  express  purpose  of 
measuring  physical  factors  in  different  habitats  was  that  of  Clements 
(1907  :287;  19072  :  65),  who  employed  potometers  of  native  species  for 
determining  the  efficiency  of  the  factors  involved  in  altitude,  and  potted 
sunflowers  as  standard  plants  to  supplement  the  instrumental  readings  in 
different  serai  habitats.  Sampson  and  Allen  (1909  :  45)  used  potometer 
batteries  of  native  species  to  determine  the  comparative  transpiration  of 
four  habitats  provided  with  instruments,  as  well  as  to  measure  the  reciprocal 
water-loss  of  sun  and  shade  forms  of  the  same  species,  and  the  effect  of 
altitude  on  transpiration. 

Planting  in  different  situations  to  determine  the  comparative  behavior 
of  seedlings  has  been  practiced  chiefly  by  foresters.  Pearson  (1914  :  253) 
employed  seedlings  of  Douglas  fir  to  ascertain  the  effect  of  aspen  cover  on 


HISTORICAL. 


7 


establishment  and  growth,  placing  100  plants  in  each  of  two  plots  in  the 
open  and  two  under  aspen.  The  greater  success  under  aspen  was  ascribed 
to  reduced  transpiration,  as  indicated  by  the  fact  that  evaporation  was  50 
to  100  per  cent  less.  In  a  study  of  the  subclimax  nature  of  aspen  forest, 
Baker  (1916  :  294)  made  use  of  yellow  pine,  Douglas  fir,  Engelmann 
spruce,  and  Norway  spruce,  planting  them  in  several  light  intensities  from 
0.09  to  1.  With  the  exception  of  the  intolerant  yellow  pine,  which  did  best 
at  0.3,  ecesis  increased  with  decreased  light  and  was  greatest  at  the  lowest 
intensity.  Hole  and  Singh  (1916  :  241)  installed  experimental  quadrats 
in  sal  forests  to  determine  the  effect  of  aeration  and  light  upon  the  germi¬ 
nation  and  growth  of  sal  seeds.  The  open  plots  gave  48  per  cent  of 
germination  and  21  per  cent  of  healthy  plants  in  contrast  to  26  and  2  per 
cent  respectively  for  the  shade  ones.  Similar  quadrats  were  employed  to 
disclose  the  consequences  of  removing  the  forest  cover,  the  shade  and 
cleared  plots  giving  respectively  71  and  91  per  cent  of  germination  and  34 
and  51  per  cent  of  healthy  plants,  height  growth  in  the  open  being  2.5  times 
as  great.  Iljin  (1916  :  65)  made  use  of  potometers  to  determine  the  tran¬ 
spiration  and  photosynthesis  of  various  mesophytes  and  xerophytes  in 
different  habitats,  and  McLean  (1919)  employed  leaf  potometers  for  water- 
loss  in  rain-forests. 

Beginning  with  1916,  the  use  of  standard  plants  as  instruments  under¬ 
went  further  development  (Clements,  1916  :  439;  Livingston  and  McLean, 
1916  :  362).  The  first  extensive  investigation  was  that  of  McLean 
(1917  :  129),  which  was  “an  attempt  to  test  certain  methods  for  determining 
some  of  the  quantitative  relations  between  climatic  conditions  and  the 
growth  of  plants.  The  plant  is  thus  regarded  as  a  sort  of  integrating  and 
recording  instrument,  the  reading  of  which  is  zero  at  the  beginning  of 
each  observation  period.,,  The  standard  plant  employed  was  soy-bean 
grown  from  seed  for  each  observation  period.  The  plants  were  all  grown 
in  the  same  soil  in  pots  furnished  with  auto-irrigators,  and  in  consequence 
temperature,  evaporation,  and  sunshine  were  the  conditions  studied.  The 
two  stations  considered  were  Oakland  in  the  mountains  of  western  Mary¬ 
land  and  Easton  on  the  eastern  shore  of  Chesapeake  Bay.  The  growth 
measurements  taken  each  month  were  stem-height,  average  number  of 
leaves  per  plant,  average  length  and  width  of  mature  leaves,  and  average 
of  the  products  obtained  by  multiplying  length  by  width  for  each  leaf,  sup¬ 
plemented  by  average  leaf-area  and  average  dry  weight  of  tops  per  plant. 
It  was  found  that  temperature  was  the  limiting  condition  for  growth  during 
the  first  two  weeks,  while  the  moisture  relation  was  largely  controlling  for 
the  second  two  weeks,  especially  when  the  temperature  was  high. 

Weaver  and  Thiel  (1917  :  47)  employed  woody  seedlings  as  well  as 
potometers  to  measure  the  transpiration  relations  of  prairie,  scrub,  and 
forest  at  Lincoln  and  Minneapolis.  A  considerable  number  of  native  trees 
and  shrubs  were  utilized,  comprising  Quercus  macrocarpa,  Acer  sacchar- 
inum,  A.  negundo,  Ulmus  americana,  Fraxinus  lanceolata,  Prunus  serotina, 
and  Rosa  arkansana.  Both  sun  and  shade  forms  were  used  in  the  case  of 
the  latter.  Marked  differences  were  disclosed  between  the  various  com¬ 
munities;  for  example,  the  transpiration  in  oak  forest  was  less  than  a  half 


8 


THE  PHYTOMETER  METHOD. 


of  that  in  hazel  scrub,  and  the  water-loss  in  the  latter  less  than  a  third  of 
that  in  the  prairie.  The  most  significant  fact  was  the  wide  discrepancy 
between  evaporation  as  determined  by  the  porus-cup  atmometer  and  the 
transpiration  from  phytometers,  amounting  in  some  cases  to  100  per  cent. 
The  series  of  studies  designed  to  develop  the  phytometer  as  a  basic  method 
in  quantitative  ecology  was  begun  in  1918,  and  preliminary  accounts  of  its 
progress  have  been  made  from  year  to  year,  as  follows:  Clements  and 
Weaver,  1918;  Clements,  Weaver,  and  Goldsmith,  1919,  1920,  1921,  1922; 
Clements  and  Goldsmith,  1923;  Clements,  1920  :  42,  45,  70. 

Sampson  (1918)  has  made  the  most  comprehensive  investigation  of 
habitat  factors  on  the  basis  of  standard  plants,  employing  Pisum  sativum , 
Triticum  durum,  and  Bromus  marginatus  for  this  purpose.  The  climatic 
factors  concerned  were  those  of  the  Petran  chaparral  above  6,500  feet,  the 
montane  forest  above  7,500  feet,  and  the  subalpine  forest  from  9,000  to 
11,000  feet,  the  stations  being  located  at  7,100,  8,700,  and  10,000  feet. 
Leaves  and  stems  were  measured  first  at  10-day  and  then  at  monthly 
intervals,  and  the  dry  wreight  and  ash-content  were  determined  at  the  end 
of  the  growing  season.  The  water  requirement  was  found  to  be  greatest 
in  the  chaparral,  less  in  the  subalpine  forest,  and  least  in  the  montane 
climax,  while  the  length  of  stem  was  also  greatest  in  the  chaparral  and 
least  in  the  montane  type,  the  production  of  dry  matter  being  just  reversed. 
An  especially  significant  result  lay  in  the  indications  as  to  cropping  possi¬ 
bilities  furnished  by  the  Kubanka  wheat  and  Canadian  field  pea. 

The  development  of  transplant  phytometers  in  contrast  to  the  use  of 
standard  plants  was  begun  in  1919,  and  the  essentials  of  the  method  are 
now  practically  complete  (Clements  and  Weaver,  1919-1923;  cf.  Experi¬ 
mental  Vegetation,  1924).  The  climatic  series  comprises  stations  ranging 
from  a  rainfall  of  35  inches  in  eastern  Nebraska  to  one  of  15  inches  at 
Colorado  Springs,  while  the  edaphic  runs  from  swamp  at  the  hydrophytie 
extreme  through  low  and  high  prairie  to  gravel-knoll  and  salt-flat  at  the 
xerophytic  end.  In  addition,  the  two  transects  for  experimental  evolution, 
the  Petran  at  Pike’s  Peak  and  the  Sierran  from  the  Pacific  Coast  through 
the  Sierra  Nevada  to  the  desert,  also  yield  phytometric  data  of  great 
climatic  value.  To  the  same  general  category  belong  clip  and  production 
quadrats,  which  serve  to  compare  the  efficiency  of  different  regions,  seasons, 
or  years  (Weaver,  1921:400;  1924;  Taylor  and  Loftfield,  1922;  1923). 
Finally,  a  combination  of  phytometer  methods  has  been  employed  in  the 
analysis  of  the  factor-complex  on  opposite  slopes  at  the  Alpine  Laboratory 
(Clements  and  Lutjeharms,  1921,  1922;  Lutjeharms,  1924). 

Hildebrandt  (1921  :  341)  has  presented  a  complete  account  of  the 
investigation  into  climatic  conditions  and  plant  growth  made  by  McLean, 
who  reported  the  results  for  two  stations,  as  already  indicated  (p.  7). 
Nine  stations  were  concerned,  and  the  standard  plant  employed  was  the 
soy-bean.  The  factors  determined  were  air  temperature,  evaporating  power 
of  the  air,  and  sunlight  intensity  and  duration,  while  the  plant  measure¬ 
ments  taken  were  stem-height,  leaf-area,  leaf-product,  and  dry  weight. 
Johnston  (1921  :  41)  has  made  a  similar  study  of  the  atmospheric  con¬ 
ditions  of  a  greenhouse  with  respect  to  an  unshaded  portion  and  a  cheese- 


KINDS  OF  PHYTOMETERS. 


9 


cloth  shade-tent.  Plants  of  buckwheat  were  used  as  standards,  being 
grown  for  4-week  periods  through  13  months.  The  factors  measured  were 
temperature,  evaporation,  and  radiation,  and  the  plant  responses  deter¬ 
mined  at  regular  intervals  were  stem-height,  leaf-area,  transpiration,  and 

dry  weight. 

KINDS  OF  PHYTOMETERS. 

As  is  evident,  the  term  phytometer  {^vtov,  plant;  ylrpov,  measure)  de¬ 
notes  a  plant  measure,  and  is  employed  for  either  a  single  plant  or  a  plant 
group.  In  general,  the  distinction  between  the  two  types  is  convenient  if 
not  natural,  but  it  must  be  recognized  that  individual  phytometers  are 
regularly  arranged  in  batteries  of  several  to  many,  while  group  phytometers 
may  often  be  analyzed  into  individuals.  Moreover,  it  is  sometimes  desirable 
to  grow  more  than  one  plant  in  a  single  container.  The  difference  is  most 
clearly  shown  by  standard  plants  in  sealed  containers  on  the  one  hand  and 
by  clip,  crop,  or  transplant  quadrats  on  the  other.  Phytometers  may  fur¬ 
ther  be  distinguished  as  natural  when  native  plants,  or  indicators,  are 
utilized  in  position,  and  as  artificial  when  they  are  specially  grown  or  trans¬ 
planted  as  measures.  Control  phytometers  are  those  in  containers,  which 
permit  the  control  of  one  or  more  factors,  especially  in  the  soil,  and  allow 
the  plants  to  be  moved  about  for  checking  or  transferring.  Free  phyto- 
meters  are  planted  in  the  soil  and  are  subject  to  the  factor-complex  of  the 
habitat,  though  a  certain  amount  of  control  may  be  exerted  by  means  of 
watering,  shading,  covering,  etc.  Climatic  phytometers  are  those  in  which 
the  effect  of  soil  factors  is  eliminated  by  rendering  these  uniform  in  sealed 
containers,  while  edaphic  ones  are  characterized  by  different  soil  habitats 
within  the  same  local  climate. 

CONTROL  PHYTOMETERS. 

These  consist  of  cultivated  or  native  species  in  sealed  or  open  containers. 
With  sealed  containers  the  effect  of  rainfall  is  eliminated  and  the  direct 
factors  concerned  are  humidity,  temperature,  and  light.  Open  containers 
with  the  same  soil  give  the  total  climatic  effect,  and  when  checked  against 
sealed  ones  furnish  evidence  of  the  influence  of  varying  rainfall  through 
the  direct  factor,  water-content.  If  open  containers  with  soils  from  the 
different  habitats  are  added  to  the  battery,  it  becomes  possible  to  dis¬ 
tinguish  the  effects  of  air  and  soil  factors.  Still  further  differentiation  of 
the  control  is  possible,  but  at  present  it  is  desirable  only  with  crop  plants. 

It  seems  preferable  to  restrict  the  term  standard  plant  or  standard  phy¬ 
tometer  to  cultivated  species,  since  these  are  readily  obtained  and  grown 
in  nearly  all  regions.  They  are  likewise  more  dependable  than  native 
species,  as  most  of  the  latter  require  a  special  study  before  satisfactory 
germination  and  growth  can  be  secured.  For  this  reason  cultivated  plants 
are  especially  desirable  when  growth  is  one  of  the  responses  to  be  measured. 
It  is  obvious  that  they  should  be  employed  when  phytometers  are  to 
furnish  information  with  reference  to  cropping  possibilities  and  methods. 
For  this  purpose  the  preferred  species  is  the  one  actually  to  be  grown,  or 
one  as  nearly  like  it  as  possible  in  its  demands.  In  accordance  with  the 


10 


THE  PHYTOMETER  METHOD. 


same  principle,  native  plants  should  be  used  in  the  study  of  forest  and 
range,  a  widespread  species  such  as  Pinus  ponderosa  or  Stipa  comata  being 
preferable  for  climatic  comparisons.  In  phytometer  batteries  the  widest 
range  of  results  is  obtained  by  the  use  of  both  cultivated  and  native  plants. 

TRANSPLANT  PHYTOMETERS. 

Free  phytometers  may  be  grown  in  place,  or  transferred  from  another 
habitat  or  the  greenhouse  in  which  they  have  been  started.  When  the 
whole  process  of  ecesis  is  to  be  taken  into  account,  seeding  is  imperative, 
but  the  greater  certainty  obtained  by  the  use  of  plants  causes  transplanting 
to  be  the  more  profitable  method,  particularly  when  physical  factors  alone 
are  to  be  measured.  If  the  total  effect  of  the  habitat  is  to  be  analyzed  in 
terms  of  factors,  competition,  and  animals,  both  seeds  and  transplants  must 
be  employed.  When  habitats,  local  or  formational,  are  to  be  compared, 
plants  are  subjected  to  the  total  impact  of  the  factor-complex,  but  some 
degree  of  control  is  necessary  to  determine  the  influence  of  particular 
factors  or  to  enable  seedlings  or  transplants  to  pass  the  initial  stage  success¬ 
fully.  This  is  secured  by  watering,  aerating,  shading,  thinning,  covering 
against  frost  or  winter-killing,  etc.  A  further  degree  of  control,  and  hence 
of  analysis,  is  obtained  by  seeding  or  planting  in  soil-pockets  or  in  quadrats 
made  uniform  as  to  soil,  or  in  the  different  natural  soils  of  the  same  climate. 
The  methods  and  technique  of  transplant  phytometers  have  been  worked 
out  in  detail  in  connection  with  the  three  climatic  and  one  edaphic  experi¬ 
mental  transects  already  mentioned,  but  their  discussion  is  to  be  found  in 
the  volume  on  experimental  vegetation  (Clements  and  Weaver,  1924). 

INDICATOR  PHYTOMETERS. 

Every  indicator  plant  is  a  potential  phytometer  of  greater  or  less  value, 
requiring  only  measurements  and  factor  readings  to  convert  it  into  an 
actual  one.  In  nature  these  measure  the  total  habitat,  but  they  may  b$ 
treated  very  like  transplant  phytometers  to  yield  various  degrees  of 
analysis.  They  may  be  protected  to  give  total  growth  unaffected  by 
grazing,  or  watered  or  covered  to  equalize  certain  factors.  They  may  even 
be  replaced  in  uniform  soil  to  disclose  the  climatic  effect,  when  they 
approximate  transplant  phytometers.  They  permit  measurements  of 
growth,  photosynthesis,  or  respiration  as  readily  as  do  control  phytometers, 
but  they  must  be  cut  out  in  soil-boxes  to  furnish  transpiration  weighings. 
Indicator  plants  possess  the  unique  value  of  being  already  established,  as 
well  as  adapted  to  conditions,  and  for  this  reason  afford  a  helpful  check 
upon  transplant  and  control  phytometers. 

COMMUNITY  PHYTOMETERS. 

These  consist  of  a  group  of  individuals  of  one  or  more  species  in  the 
reciprocal  relation  to  each  other  that  obtains  in  a  natural  community  or  in 
a  cultivated  field.  They  may  vary  much  in  size,  but  that  of  the  meter 
quadrat  possesses  distinct  advantages.  Like  individual  phytometers,  they 
may  be  either  natural,  planted,  or  transplanted,  or  even  employed  in  con¬ 
tainers,  though  the  latter  form  has  as  yet  been  little  developed.  The  clip- 


KINDS  OF  PHYTOMETERS. 


11 


quadrat  constitutes  the  best  example  of  the  natural  phytometer,  as  the 
growth  habit  of  grasses  makes  this  much  more  useful  than  a  cut-quadrat  in 
scrub  or  forest.  In  the  natural  condition  it  furnishes  a  measure  of  the 
combined  influence  of  factors,  competition,  and  animals,  but  it  may  be  so 
controlled  by  protection  as  to  eliminate  the  latter,  or  to  equalize  certain 
factors.  It  is  much  more  difficult  to  remove  competition,  and  the  role  of 
the  latter  can  best  be  determined  by  means  of  individual  phytometers,  in 
which  competition  is  lacking.  The  transplanting  of  communities  to  serve 
as  phytometers  is  practicable  only  in  the  case  of  cryptogams,  especially 
lichens  and  mosses,  small  or  seedling  families  and  colonies,  or  portions  of 
herbaceous  communities,  particularly  of  the  sod-forming  type.  In  moving 
meter  quadrats  of  alpine  meadow  from  the  summit  of  Pike’s  Peak  to  the 
Alpine  Laboratory,  it  was  necessary  to  divide  them  into  smaller  squares, 
and  this  would  be  even  more  imperative  in  the  case  of  taller  or  deeper- 
rooted  vegetation.  While  scrub  and  tree  groups  can  be  transplanted  in  the 
seedling  stage,  the  labor  is  so  great  that  it  is  much  more  feasible  to  use 
seeding  or  planting  quadrats  for  the  results  desired.  Such  quadrat  phy¬ 
tometers  are  essentially  alike  in  nature  and  treatment,  whether  located 
in  forest,  range,  or  cultivated  field.  They  are  usually  more  successful  in 
the  latter,  owing  to  the  use  of  cultivated  plants,  protection  against  mishaps, 
and  the  opportunity  for  further  control. 

RESPONSES  MEASURED. 

Functions  permit  of  readier  and  more  exact  measurement  than  changes 
of  structure,  while  growth  offers  peculiar  advantages  as  a  process  inter¬ 
mediate  between  the  two.  Naturally,  such  functions  as  transpiration  and 
photosynthesis,  which  are  controlled  by  highly  variable  factors — water, 
light,  and  temperature — are  much  more  significant  than  respiration.  For 
evaluating  the  relative  efficiency  of  holard  and  humidity,  transpiration  is 
of  paramount  importance,  especially  when  stomatal  behavior  is  taken  into 
consideration.  In  the  case  of  light,  photosynthesis  is  similarly  all- 
important.  Rate  of  growth  and  total  growth,  expressed  in  various  forms, 
reflect  both  transpiration  and  photosynthesis,  but  the  great  value  lies  in  the 
fact  that  growth  sums  up  the  effect  of  practically  all  factors.  It  may  be 
measured  at  regular  intervals  in  terms  of  stem  and  leaf,  or  expressed  at  the 
end  as  dry  weight  or  water  requirement.  It  also  appears  as  seed-production 
and  germination,  the  former  being  of  the  greatest  significance  with  crop 
phytometers.  When  the  impact  of  factors  induces  a  qualitative  change  in 
growth,  it  results  in  adaptation,  in  terms  of  form  or  structure,  or  both,  and 
this  is  definitely  measurable,  though  it  still  lacks  a  proper  system  of  units. 
Adaptation  may  likewise  operate  on  the  reproductive  system,  though  less 
readily,  and  the  flower  affords  further  measures  of  the  habitat,  especially 
as  to  methods  of  pollination. 

For  the  usual  range  of  habitat  measurements,  the  most  serviceable 
phytometers  are  those  for  transpiration,  photosynthesis,  growth,  and 
adaptation.  The  simplest,  most  convenient,  and  widely  useful  is  the  tran¬ 
spiration  phytometer,  as  water-loss  is  the  most  variable  and  easily  measured 
of  functions.  As  the  sum  of  all  functions,  growth  furnishes  the  best  single 


12 


THE  PHYTOMETER  METHOD. 


phytometer  of  the  total  effect  of  habitat,  while  the  difficulties  of  field 
application  still  leave  something  to  be  desired  in  the  case  of  photosynthesis. 
For  thoroughgoing  and  comprehensive  investigation,  the  phytometer  bat¬ 
tery  should  contain  plants  assigned  to  each  of  the  three  determinations 
when  these  can  not  be  safely  carried  out  on  each  plant.  This  is  necessary 
also  for  adaptation  when  the  dry  weight  of  plants  is  regularly  determined. 

NATURE  AND  ROLE  OF  ZOOMETERS. 

As  members  of  the  same  community,  animals  resemble  plants  in  that 
they  can  also  be  employed  as  measures  of  certain  factors  and  relations. 
Because  of  their  motility  and  the  absence  of  the  photosynthetic  mechanism, 
they  are  much  less  affected  by  direct  factors,  with  the  exception  of  tem¬ 
perature.  The  latter  is  probably  the  most  effective  physical  factor  in  the 
case  of  land  animals  at  least,  though  the  actual  order  of  efficient  factors 
must  await  quantitative  physiological  analysis.  Even  more  controlling  is 
the  biotic  factor  of  food-supply,  and,  in  many  cases,  of  materials  and 
shelter.  It  is  obvious  that  these  can  be  directly  measured,  while  the  climate 
must  at  present  be  determined  as  a  complex  in  which  temperature  and 
humidity  are  probably  most  important.  In  the  case  of  burrowing  and 
other  soil  animals  it  is  probable  that  soil  texture,  aeration,  and  other 
factors  may  be  measured  to  some  degree.  In  aquatic  habitats,  which  con¬ 
sist  essentially  of  one  medium,  temperature,  light,  aeration,  acidity,  and 
salt-content  are  all  susceptible  of  measurement. 

Zoometers  {£6oov,  animal;  / icrpov ,  measure)  may  be  distinguished  on  the 
basis  of  objective  as  climatic  or  factor,  food,  or  pollination  measures.  The 
latter  is  obviously  a  food  relation  also,  but  of  such  a  highly  specialized  sort 
as  to  deserve  recognition.  With  respect  to  method,  zoometers  may  be 
designated  as  indicator,  transfer,  and  introduction.  The  first  deals  with 
the  response  of  animals  in  the  natural  community,  the  second  with  the 
response  in  a  new  but  related  or  adjacent  habitat,  and  the  third  with 
that  of  domesticated  or  exotic  animals.  In  all  of  these  the  method  of 
exclosures  and  inclosures  is  fundamental.  By  the  exclosure  is  understood 
an  area  fenced  against  all  or  selected  species  and  with  all  or  certain  of  the 
animals  within  it  exterminated,  while  the  inclosure  is  similarly  treated, 
except  that  a  certain  number  of  animals  are  placed  in  it. 

ESSENTIALS  OF  THE  PHYTOMETER  METHOD. 

The  fact  that  standard  plants  must  be  grown  in  sealed  containers  and 
placed  in  different  and  often  extreme  habitats  demands  that  the  species 
used  should  be  as  hardy  and  vigorous  as  possible.  These  requirements  are 
usually  best  met  by  cultivated  plants  and  weeds,  and  among  native  species 
by  those  of  subruderal  habit  which  readily  invade  bare  areas.  Because  of 
the  measurements  required,  species  with  simple  entire  leaves  or  large 
leaflets  are  to  be  preferred,  such  as  the  grains,  sunflower,  and  bean.  It  is 
especially  desirable  that  the  individuals  should  be  alike  in  size  and  form, 
and  as  uniform  in  response  as  possible.  The  latter  can  only  be  determined 
by  preliminary  readings,  but  this  is  imperative  when  each  battery  contains 
a  small  number  of  individuals.  When  there  is  a  large  number  to  select 


ESSENTIALS. 


13 


from,  those  with  a  wide  departure  are  rejected,  but  with  a  limited  number, 
as  is  often  the  case  with  natives,  the  individuals  are  assigned  to  each 
battery  in  such  a  way  as  to  give  the  same  average  response.  Six  con¬ 
stitutes  an  adequate  number  of  individuals  of  each  species  when  all  are  to 
be  carried  through,  but  10  is  better  when  short-period  readings  are  also  to 
be  made.  The  number  of  species  in  a  habitat  battery  will  be  determined 
by  the  results  sought  and  the  assistance  available.  In  the  case  of  standard 
plants  used  only  for  measuring  transpiration  or  photosynthesis,  a  single 
species  may  suffice,  but  for  comprehensive  results  3  is  a  minimum,  and  5 
or  6  may  be  used  to  advantage. 

The  size  of  containers  will  be  determined  by  several  considerations, 
chiefly  the  size  of  the  plants  and  especially  the  root  systems,  the  region, 
and  the  help  available.  In  the  Pike’s  Peak  region  small  containers  are 
feasible  because  of  the  relatively  low  temperatures  and  short  season  and 
almost  imperative  because  of  the  difficulties  of  transportation.  In  the 
Middle  West,  with  long  seasons  and  high  temperatures,  containers  must  be 
several  times  larger,  1  to  2  feet  wide  and  several  feet  deep,  to  afford  space 
for  the  roots.  Since  the  containers  must  be  impervious,  tin,  zinc,  or  gal¬ 
vanized  iron  is  demanded.  The  seal  presents  greater  difficulties,  as  it  must 
shed  rain,  should  not  crack  or  injure  the  stem  of  the  plant,  arid  be  capable 
of  being  applied  with  the  minimum  of  time  and  expense.  Much  experi¬ 
menting  has  been  done  in  this  connection,  the  outcome  of  which  is  given 
later.  In  the  case  of  free  phytometers  the  precautions  to  be  taken  are  those 
indicated  by  the  best  nursery  practice  of  the  forester  or  florist. 

While  the  number  and  location  of  stations  will  be  determined  by  the 
problem,  it  is  obvious  that  at  least  two  are  required  for  comparative  values 
and  that  the  habitats  should  show  distinct  differences  in  terms  of  indicators. 
Mountain  regions  afford  peculiar  opportunities  for  a  climatic  series  because 
of  the  sharp  gradient  in  a  short  distance,  and  serai  habitats,  as  from  pond 
to  grassland  or  forest,  offer  the  best  range  of  edaphic  conditions.  The 
instrumental  measurement  of  each  habitat  should  be  as  complete  as  pos¬ 
sible.  The  battery  should  regularly  contain  a  hygro-thermograph,  sela- 
graph,  anemometer,  and  rain-gage,  and  preferably  a  soil-thermograph  and 
atmometer,  and  in  addition,  determinations  of  holard,  soil-air,  and  solutes 
should  be  made  whenever  free  phytometers  are  included  in  the  series. 
Hygro-thermographs  have  been  regularly  placed  in  instrument  shelters  of 
the  usual  Weather  Bureau  type.  The  installation  has  been  so  organized 
that  weekly  visits  suffice,  at  least  for  distant  stations.  The  phytometers 
and  instruments  at  each  station  are  protected  by  a  rodent-proof  fence,  but 
are  fully  exposed  to  the  habitat  above. 

The  major  responsibility  for  the  field  work  during  1918  was  taken  by 
Professors  J.  E.  Weaver  and  F.  C.  Jean,  and  acknowledgment  is  also  due 
Dr.  Dolly  Lutjeharms,  Professor  T.  J.  Fitzpatrick,  Dr.  Lee  Bonar,  and  Mr. 
J.  R.  Bruff  for  their  work  during  the  other  seasons. 


CLIMAXES  AND  CLIMATES  OF  THE  PIKE’S 

PEAK  REGION. 

Pike’s  Peak  arises  abruptly  from  the  Great  Plains  at  an  altitude  of  6,000 
feet  to  a  height  of  14,142  feet,  in  a  distance  little  more  than  7  miles  by  air¬ 
line.  It  is  perhaps  unique  on  the  North  American  continent  in  this  respect, 
as  it  also  is  in  the  fact  that  transport  by  rail  is  available  for  the  entire 
distance.  Moreover,  its  location  below  the  thirty-ninth  parallel  in  a  great 
grassland  climax  with  relatively  low  rainfall  has  permitted  a  greater 
differentiation  of  climates  and  climaxes  on  its  slopes  than  is  found  on  any 
other  mountain  of  the  continent.  The  region  possesses  the  further  advan¬ 
tage  that  quantitative  studies  in  ecology  were  begun  here  in  1899  and  have 
been  carried  on  continuously  since. 

The  visible  zones  from  base  to  top  are  four,  namely,  grassland,  chaparral, 
forest,  and  alpine  meadow,  but  the  forest  zone  comprises  three  climaxes. 
The  series  thus  contains  six  climaxes,  beginning  with  mixed  prairie  and 
extending  through  chaparral,  woodland,  montane  forest,  and  subalpine 
forest  to  alpine  meadow.  The  chaparral,  consisting  of  Quercus,  Cerco- 
carpus,  and  Rhus ,  is  much  fragmented  in  this  region  and  the  woodland  of 
Pinus  edulis  and  Juniperus  is  near  its  northern  limit,  so  that  stations  were 
not  maintained  in  them  after  the  first  season. 

MIXED  PRAIRIE. 

This  climax  receives  its  name  from  the  fact  that  it  comprises  both  tail- 
grasses  and  short-grasses,  giving  it  a  typical  two-layered  structure,  in 
contrast  to  the  other  associations  of  the  grassland  formation.  Over  much 
of  its  area  the  tail-grasses  have  been  much  reduced  or  entirely  removed  by 
grazing,  so  that  the  community  often  consists  of  a  low,  usually  dense  cover 
of  short-grasses  belonging  to  the  genera  Bouteloua  and  Bulbilis.  Of  the 
dominants  previously  indicated  for  the  mixed  prairie  and  short-grass  plains 
(Plant  Indicators,  pp.  135,  139),  which  are  now  regarded  as  the  same 
climax,  nearly  all  are  to  be  found  on  the  plains  at  the  foot  of  the  mountains. 
Of  the  tail-grasses  the  most  important  are  Stipa  comata,  Agropyrum 
glaucum,  and  Sporobolus  cryptandrus,  while  the  chief  short-grass  is  Boute¬ 
loua  gracilis  (plate  2a).  Bulbilis  dactyloides,  the  regular  codominant  of 
the  latter  to  the  eastward,  is  here  found  only  in  occasional  playa-like 
depressions.  The  postclimax  Andropogons,  A.  scoparius,  furcatus,  and 
nutans,  are  often  abundant  and  sometimes  dominant  in  areas  with  higher 
holard,  such  as  valleys,  mesas,  and  stable  sandhills.  The  number  of  sub- 
dominants  is  nearly  as  great  as  in  the  true  prairies,  but  the  individuals  are 
less  abundant  and  luxuriant,  and  the  societies  much  less  mixed.  The  most 
widespread  societies  in  the  spring  are  Aragalus  lamberti,  Sophora  sericea, 
and  Senecio  aureus,  of  the  summer  Psoralea  tenuiflora,  Lepachys  colum- 
naris,  and  Haplopappus  spinulosus,  and  of  the  autumn  Artemisia  jrigida 
and  campestris,  Gutierrezia  sarothrae,  Grindelia  squarrosa,  Liatris  punctata, 
and  Carduus  undulatus. 

The  climax  stage  occupies  more  than  nine-tenths  of  the  area.  The 
hydrosere  is  limited  to  a  few  artificial  ponds  and  lakes,  characterized  chiefly 
by  the  Scirpus-Typha  associes,  while  the  xerosere  is  confined  to  the  cliffs 

14 


MONTANE  FOREST. 


15 


and  talus  of  the  mesa  escarpments.  Subseres  are  found  primarily  in  sand¬ 
hills  and  sandy  plains,  and  to  some  extent  in  fallow  fields  and  overgrazed 
pastures.  The  former  are  chiefly  in  the  subclimax  stage  marked  by  Andro- 
pogon  halli  and  scoparius  and  Artemisia  filifolia,  often  with  much  Cala- 
movilja  longijolia  and  Elymus  canadensis.  The  first  climax  grasses  to 
enter  are  usually  Sporobolus  and  Stipa,  followed  by  Bouteloua.  Overgrazed 
areas  are  characterized  by  the  absence  of  the  tail-grasses  and  the  increasing 
abundance  of  Muhlenbergia  or  Aristida,  and  in  the  later  stages  by  the 
dominance  of  Artemisia  frigida  or  Gutierrezia,  or  by  both. 

The  rainfall  is  approximately  15  inches  in  this  portion  of  the  climax, 
with  an  amplitude  of  8  to  22  inches.  The  mixed  prairie  is  chiefly  in  con¬ 
tact  with  the  chaparral,  which  breaks  up  into  numerous  miniature  groves 
over  an  ecotone  often  one  to  several  miles  wide.  However,  the  broken 
topography  and  the  cyclic  variation  in  rainfall  bring  the  grassland  also  in 
contact  with  the  woodland  and  the  montane  forest,  with  which  it  forms 
characteristic  and  extensive  savannah  at  altitudes  of  6,000  to  7,000  feet. 

MONTANE  FOREST. 

This  climax  is  a  coniferous  forest  extending  generally  from  7,000  to  9,000 
feet.  The  major  dominants  are  Pinus  ponderosa,  Pseudotsuga  mucronata, 
and  Abies  concolor,  with  Picea  pungens  and  Pinus  fleorilis  scattered  or 
locally  prominent  (plate  2b).  In  this  region  the  three  dominants  prac¬ 
tically  never  meet  on  equal  terms,  Pinus  taking  the  drier  warmer  slopes 
and  Pseudotsuga  and  Abies  the  moister  cooler  ones.  However,  they  do  mix 
sufficiently  to  prove  that  there  is  no  climax  difference  between  them.  The 
yellow  pine  forms  pure  stands  in  the  lower  portion  of  the  zone,  the  white 
fir  in  the  middle,  and  the  Douglas  fir  in  the  upper  part,  the  last  two  often 
making  a  mixed  forest  also.  Fire  has  occurred  more  frequently  in  the 
open  canyons,  and  these  have  come  to  be  occupied  by  open  aspen  forest 
with  a  striking  herbaceous  undergrowth,  consisting  of  Geranium ,  Calo- 
chortus,  Campanula,  Pentstemon,  Rudbeckia,  Valeriana,  etc.  Societies  are 
much  less  developed  in  the  climax  forest,  the  primeval  portions  often 
containing  only  scattered  clans  of  shade  forms  and  saprophytes.  Among 
the  most  important  subdominants  of  the  typical  forest  are  Mertensia, 
Thalictrum,  Chamaenerium,  Castilleia,  Erigeron,  Zygadenus,  etc.  (Plant 
Indicators,  207). 

About  a  third  of  the  area  of  the  montane  zone  is  covered  by  the  climax, 
another  third  by  aspen,  and  the  remainder  by  serai  communities.  The 
hydrosere  is  little  in  evidence,  and  the  subsere  is  represented  almost  wholly 
by  the  burn  succession.  The  rock  xerosere  is  much  the  most  important,  the 
stages  most  in  evidence  being  the  gravel-slide  of  bunch  and  mat  herbs  and 
the  half  gravel-slide  dominated  by  grasses.  The  grass  and  scrub  stages  are 
best  developed  on  the  southerly  slopes,  and  are  composed  chiefly  of  domi¬ 
nants  from  the  chaparral  and  mixed  prairie  that  migrated  upward  during 
the  dry  phase  of  the  climatic  cycle.  At  its  upper  edge  the  montane  forest 
lies  in  contact  with  the  subalpine  climax,  while  below  it  is  usually  in  touch 
with  woodland,  though  it  frequently  meets  chaparral  and  grassland  also. 
The  average  rainfall  is  about  21  inches,  with  an  amplitude  of  15  to  26 
inches.  Two-thirds  of  the  total  falls  between  April  1  and  August  31,  as 


16 


CLIMAXES  AND  CLIMATES. 


is  likewise  true  of  the  glassland  climax,  owing  to  the  summer  type  of 
precipitation. 

SUBALPINE  FOREST. 

This  is  a  coniferous  forest  resembling  the  preceding  in  many  respects,  but 
consisting  of  a  single  great  dominant  in  the  Pike’s  Peak  region.  While  the 
Petran  subalpine  climax  is  regularly  constituted  by  Picea  engelmanni  and 
Abies  lasiocarpa,  the  latter  is  lacking  here  and  the  forest  is  pure  for  the 
most  part,  Pinus  aristata  becoming  more  or  less  abundant  as  timber-line 
is  approached  and  P.  fiexilis  appearing  along  rocky  ridges  (plate  3a)  .  The 
lodgepole  pine,  P.  contorta,  which  covers  much  of  this  zone  northward  as 
a  burn  subclimax,  is  also  absent,  and  the  extensive  burns  are  covered  with 
aspen  in  consequence.  The  societies  of  the  forest  floor  resemble  those  of 
the  montane  climax,  belonging  to  the  same  genera  for  the  most  part,  but 
are  less  dense  and  luxuriant  in  consequence  of  the  shorter  season  (Plant 
Indicators,  224). 

The  annual  rainfall  is  approximately  25  inches,  with  an  amplitude  of  18 
to  33  inches,  and  the  mean  temperature  36°  F.  The  greater  rainfall  and 
smaller  evaporation  make  lakes  and  ponds  more  numerous,  and  the  hydro¬ 
sere  is  best  represented  in  this  climax.  The  submerged  and  floating  stages 
are  little  developed,  and  the  amphibious  ones  are  represented  only  by 
sedges  and  rushes.  The  latter  may  be  followed  by  a  wet-thicket  stage  of 
Betula  and  Salix,  or  it  may  pass  directly  into  the  grass  stage  on  better- 
drained  soil.  The  xerosere  is  confined  to  cliffs,  talus,  and  gravel-slides, 
with  the  stages  more  or  less  fragmentary. 

ALPINE  MEADOW. 

The  alpine  zone  is  occupied  by  a  climax  composed  of  sedges  and  grasses, 
for  the  most  part  but  a  few  inches  high.  The  major  dominants  are  Car  ex 
rupestris  and  filifolia,  while  a  large  number  of  species  of  Carex  and  Poa 
play  some  part.  This  climax  recalls  the  true  prairie  in  the  large  number  of 
bright-flowered  subdominants,  which  are  its  most  notable  feature.  It 
extends  from  11,000  feet  to  the  tops  of  the  highest  peaks,  above  14,000  feet, 
though  the  lower  limit  varies  much  with  the  exposure.  As  fire  and  grazing 
have  affected  this  community  but  little,  the  subsere  is  practically  absent, 
except  for  small  disturbed  areas  due  to  mining  or  water-supply  operations. 
Owing  to  the  relatively  high  rainfall,  very  low  evaporation,  and  short 
season,  lakes  and  swamps  are  abundant.  Submerged  and  floating  plants 
are  rare,  however,  and  the  hydrosere  consists  of  few  stages,  the  most 
characteristic  being  the  sedge  and  thicket  communities.  The  xerosere  is 
likewise  simple,  its  most  typical  stage  being  marked  by  cushion-plants, 
such  as  Silene  acaulis,  Androsace  chamaejasme,  Arenaria  sajanensis ,  and 
Paronychia  pulvinata  (Plant  Indicators,  232). 

The  rainfall  on  Pike’s  Peak  is  30  inches,  with  an  amplitude  of  9  to  44 
inches,  a  little  more  than  half  of  which  occurs  in  the  summer.  The  mean 
temperature  is  19°  F.,  17°  lower  than  for  the  subalpine  zone,  and  31° 
lower  than  for  the  mixed  prairie. 


METHODS  AND  RESULTS,  SEASON  OF  1918. 

Two  stations  were  installed  for  the  first  two  series  in  1918  and  continued 
for  the  third.  The  plains  station  was  located  about  5  miles  east  of  the  base 
of  the  range,  at  an  altitude  of  6,150  feet.  The  ground  is  comparatively 
level,  sloping  to  the  south  about  2°.  An  inclosure  30  by  10  meters  was 
fenced  against  cattle  by  means  of  barbed  wire,  and  a  portion  of  this  was 
protected  against  rodents  by  means  of  coarse  woven-wire  reinforced  by 
screen.  The  montane  station  was  established  on  the  south  wall  of  Engel- 
mann  Canyon,  at  an  altitude  of  8,600  feet.  The  slope-exposure  is  about 
30°  to  the  north.  The  area  was  covered  with  a  young  stand  of  Douglas 
fir  and  aspen,  which  was  cleared  for  a  space  10  meters  square  to  remove  the 
shade.  The  experimental  area  was  inclosed  with  wire  screen  6  dm.  wide 
and  of  2  mm.  mesh,  and  the  exclusion  of  rodents  was  made  complete  by 
sinking  the  screen  1  dm.  in  the  ground  and  bending  the  upper  edge  down 
obliquely  (plate  5). 


Fig.  1. — Average  temperature  (heavy  lines)  and  humidity 

(light  lines),  1918. 

For  the  third  series  three  additional  stations  were  established.  The 
gravel-slide  station  was  installed  on  the  exposed  northwest  slope  of  a  ridge 
about  100  meters  above  the  montane  station.  The  decomposed  granite  of 
the  gravel-slides  constitutes  the  most  xerophytic  habitat  of  the  montane 
climax,  with  the  exception  of  cliffs  and  rock  surfaces.  The  serai  stage  char¬ 
acteristic  of  it  consists  of  bunch  and  mat  herbs,  such  as  Aletes,  Aragalus, 
Eriogonum,  etc.,  and  the  edges  are  marked  by  dwarfed  individuals  of  Pinus 
fiexilis.  The  Douglas-fir  station  was  located  on  a  northerly  slope  at  an 
elevation  of  8,600  feet,  in  the  midst  of  the  climax  association  of  Pseudotsuga 
mucronata,  and  the  Engelmann-spruce  one  in  climax  Picea  engelmanni  of 
the  subalpine  forest,  at  an  altitude  of  9,000  feet.  No  clearing  was  made  in 
connection  with  the  last  two,  but  protection  against  rodents  was  provided 
in  the  usual  manner. 


17 


18 


SEASON  OF  1918. 


The  species  used  as  standard  plants  for  the  three  series  of  phytometers  in 
1918  were  sunflower  ( Helianthus  animus),  pinto  beans  ( Phaseolus  vulgaris), 
Kherson  oats  ( Avena  sativa) ,  Marquis  spring  wheat  ( Triticum  sativum), 
sweet  clover  ( Melilotus  alba),  and  wild  raspberry  ( Rubus  strigosus).  The 
seeds  of  the  five  cultivated  plants  were  germinated  in  flats  after  soaking 
for  12  hours  in  warm  water,  while  young  plants  of  raspberry  were  trans¬ 
planted  from  nature.  The  same  soil  was  used  throughout  the  series,  con¬ 
sisting  of  a  reddish  sandy  loam  obtained  from  a  garden  in  Manitou.  The 
analyses  of  this  soil  gave  the  results  shown  in  table  1. 


Table  1. — Phytometer  soil. 


Mechanical  analysis. 

• 

Chemical  analysis. 

Coarse  gravel .  7.1 

Fine  gravel .  0 

Coarse  sand .  15.6 

Medium  sand .  12.3 

Fine  sand .  29.3 

Very  fine  sand .  20.0 

Total  sand .  77.2 

Silt .  14.0 

Clay .  8.8 

Hygr.  coef .  5.7 

Wilt,  coef .  8.4 

Moist  equiv .  15.4 

Max.  water-content .  45.8 

P20* .  0.208 

SOs .  0.0014 

K20 .  2.36 

Fe,  Al,  Ti,  oxids .  (-) 

CaO .  (-) 

MgO .  (-) 

Si02 .  (-) 

Nitrogen .  0.130 

V olatile  matter .  3.50 

Acidity .  0 

HC1  test .  0 

The  containers  were  chiefly  cylindrical  vessels  of  galvanized  iron,  approxi¬ 
mately  6  inches  wide  by  14  inches  deep.  The  soil  used  was  run  through  a 
sieve  of  ^-inch  mesh  and  moistened  to  a  condition  of  good  tilth,  being 
worked  by  hand  to  insure  uniform  distribution  of  the  water.  About  2  cm. 
of  coarse  gravel  was  placed  in  the  bottom  of  each  container  for  a  water 
reservoir,  and  a  glass-tube  1  cm.  wide  so  adjusted  that  the  lower  end 
extended  into  the  gravel,  while  the  upper  stoppered  end  reached  just  above 
the  rim  of  the  container.  The  latter  was  then  filled  almost  to  the  top  with 
the  soil,  which  was  firmly  compacted  in  the  process.  The  dicotyl  seedlings 
were  transplanted  about  the  time  the  cotyledons  appeared,  a  single  one 
being  placed  in  the  center  and  carefully  thrust  through  a  hole  1  cm.  in 
diameter,  bored  in  a  large  flat  cork  used  as  a  stopper.  This  was  then 
sealed  by  means  of  a  wax  consisting  of  85  per  cent  paraffin  and  15  per  cent 
petrolatum,  which  was  poured  over  the  soil  surface  and  spread  evenly  by 
tilting  the  container  from  side  to  side.  The  opening  in  the  cork  around  the 
stem  was  next  filled  with  a  fine,  dry  dust-mulch,  which  prevented  evapora¬ 
tion  but  allowed  the  stem  to  grow  under  fairly  normal  conditions.  The 
cereals  were  treated  in  the  same  manner,  except  that  five  germinating  seeds 
were  placed  in  a  slit  1  by  4  cm.  cut  in  the  cork  stopper.  This  slit  was  then 
partly  filled  with  moist  soil  before  applying  the  dust-mulch. 

The  containers  were  sunk  in  the  soil  of  the  station  at  which  they  were 
to  be  grown,  so  that  the  tops  were  slightly  above  the  surface.  To  insulate 
them  from  the  extremes  of  surface  temperature,  as  well  as  to  facilitate  their 
removal  for  weighing  and  watering,  each  container  was  surrounded  by  a 


PHYSICAL  FACTORS. 


19 


collar  of  the  same  height,  but  1  inch  greater  in  diameter.  To  serve  as  a 
further  insulator  and  to  prevent  the  softening  of  the  wax  during  the  heat 
of  the  day,  the  containers  were  covered  with  a  doubled  thickness  of  woollen 
blanket,  over  which  was  placed  an  oil-cloth  one  covered  with  a  centimeter 
or  more  of  soil,  a  slit  permitting  the  stem  of  the  plant  to  protrude.  Each 
plant  was  thus  sealed  in  the  container  without  the  stem  being  touched  by 
the  wax;  the  container  was  below  the  soil  surface  but  separated  from  it 
by  an  air-jacket,  and  was  protected  from  the  heat  of  the  sun  by  triple 
insulation. 

At  intervals  the  containers  were  removed  and  weighed,  and  the  original 
weight  restored  by  the  addition  of  water  through  the  glass  tube.  At  the 
close  of  each  series  all  phytometers  were  weighed  and  the  plants  cut  at  the 
level  of  the  soil  surface.  Blue-prints  were  at  once  made  of  the  leaves  and 
the  areas  determined  later  by  means  of  the  planimeter,  and  dry  weights 
were  obtained  in  the  usual  fashion.  The  physical  factors  were  recorded 
throughout  the  season  by  means  of  standard  apparatus.  Humidity  and 
air-temperature  were  determined  by  means  of  Friez  hygro-thermographs, 
rainfall  and  wind  by  the  Weather  Bureau  rain-gage  and  anemometer,  and 
evaporation  by  the  Livingston  porous-cup  atmometer.  In  addition,  occa¬ 
sional  series  of  simultaneous  readings  were  made  at  the  various  stations  to 
determine  comparative  soil-temperatures.  Measurements  of  the  holard 
were  made  at  all  stations  at  various  depths,  though  these  did  not  bear 
directly  on  the  phytometers,  in  which  the  water-content  was  under  control. 
In  order  to  obtain  the  average  temperature  and  humidity  for  the  week  at 
each  station,  the  value  at  each  of  the  12  points  in  each  24-hour  day  where 
the  curve  intersects  the  2-hour  line  of  the  record  sheet  was  taken  and 
averaged.  The  weekly  average  for  temperature  or  humidity  was  thus 
obtained  from  84  readings  taken  at  2-hour  intervals  throughout  the  week. 
Similar  averages  were  obtained  for  day  and  night  values,  using  the  2-hour 
readings  from  8  a.  m.  to  6  p.  m.  for  the  day  and  from  8  p.  m.  to  6  a.  m.  for 
the  night. 

Temperature. 

The  decrease  of  air-temperature  with  the  altitude  is  exemplified  by  the 
summer  averages  for  the  plains  and  montane  stations.  For  the  24-hour 
day  the  drop  is  7°,  while  it  is  nearly  a  degree  greater  for  the  day  and  about 
2°  less  for  the  night.  The  greatest  differences  were  found  in  June,  when  one 
week  gave  decreases  for  the  montane  station  of  16°  for  the  24-hour  period, 
10°  for  the  night,  and  21°  for  the  day.  These  results  are  in  general  accord 
with  those  obtained  from  1903  to  1905,  when  an  average  difference  of  10° 
was  found  to  exist  between  the  plains  and  the  montane  zone.  As  would 
also  be  expected,  the  plains  exhibited  a  greater  range  of  temperature  in  the 
24-hour  period,  this  being  reflected  in  an  average  range  of  18°  in  contrast 
to  15°.  The  temperature  at  3  inches  above  the  soil-surface  decreased  more 
or  less  regularly  with  the  altitude  for  the  five  stations  from  the  plains  to 
spruce  forest,  though  exposure  and  cold-air  drainage  reversed  the  relation 
in  the  morning  to  some  degree  (fig.  1). 

In  the  case  of  soil  temperature,  there  is  likewise  a  marked  decrease  with 
altitude,  influenced  more  or  less  by  exposure  and  to  a  marked  degree  by 


20 


SEASON  OF  1918. 


cover,  as  well  as  by  depth  of  reading.  At  a  half  inch  below  the  surface  the 
average  difference  during  the  afternoon  was  more  than  10°,  while  at  a 
depth  of  4  inches  it  was  7°.  At  the  surface  there  wras  a  difference  of  17° 
between  the  montane  station  and  those  in  Douglas  fir  and  Engelmann 
spruce,  due  chiefly  to  the  removal  of  the  cover  in  the  former,  while  at  a 
depth  of  2  feet  the  difference  had  dropped  to  5°  (fig.  1). 

Humidity  and  Evaporation. 

The  average  relative  humidity  differed  but  little  between  the  two  stations, 
being  56  per  cent  on  the  plains  and  54.7  per  cent  in  the  montane  zone. 
During  the  day,  when  humidity  is  most  efficient,  it  was  nearly  4  per  cent 
less  on  the  plains  and  at  night  it  was  7  per  cent  greater.  The  daily  variation 


Plains - Montane - Gravel  slide 

. —  Douglas fir  - Engelmann  spruce 

Fig.  2. — Average  standard  evaporation,  1918. 


was  much  greater  at  the  plains  station,  namely,  21  per  cent,  in  contrast  to 
10  per  cent  (fig.  1).  As  to  wind  movement,  the  plains  led  with  a  daily 
average  of  120  miles,  the  gravel-slide  was  second  with  103  miles,  the 
montane  station  third  with  67  miles,  and  the  Douglas-fir  station  last  with 
but  29  miles,  a  result  readily  explained  by  the  forest  cover. 

Evaporation  was  obtained  by  means  of  standardized,  white,  cylindric 
atmometer  cups  set  on  non-absorbing  mounts,  placed  in  the  soil  in  such 
manner  as  to  bring  the  evaporating  surface  on  a  level  with  the  phytometers. 
The  plains  station  yielded  a  daily  average  of  47.8  c.  c.,  twice  as  great  as 
that  for  the  montane  station,  namely,  23.7  c.  c.  The  xerophytic  gravel- 
snde  was  nearly  intermediate,  33.9  c.  c.,  while  the  two  forests  were  respec¬ 
tively  13  and  9.6  c.  c.,  approximately  half  that  of  the  open  montane  station 
in  the  same  general  altitude  (fig.  2). 

Summary. 

The  plains  station  exhibited  the  highest  and  most  variable  temperatures 
of  air  and  soil,  the  most  variable  holard,  and  the  greatest  average  wind 


FIRST  SERIES. 


21 


movement.  In  the  order  of  decreasing  temperature  the  other  stations  were 
the  gravel-slide,  montane,  Douglas  fir,  and  Engelmann  spruce.  The  latter 
station  gave  the  highest  rainfall  and  holard  and  the  lowest  average  tempera¬ 
ture.  Rainfall  was  lowest  and  wind  and  evaporation  highest  at  the  plains 
station,  and  the  last  two  decreased  through  gravel-slide  and  montane  to 
Douglas  fir.  On  the  basis  of  the  usual  indirect  factors,  the  relative  humidity 
should  be  consistently  lower  at  the  plains,  but  these  were  partly  offset  by 
the  effect  of  altitude  and  of  cold-air  drainage  at  night. 

Phytometers,  First  Series. 

After  soaking  12  hours  in  warm  water,  a  quantity  of  sunflower  seeds  was 
planted  in  small  pots  of  garden  soil  at  the  montane  station  on  June  7. 
Twelve  of  the  most  vigorous  individuals  were  transplanted  into  sealed  con¬ 
tainers  at  this  station  on  June  13,  and  on  the  next  day  an  equal  number  of 
similar  plants  was  transferred  to  the  plains  station.  They  were  sunk  in 
the  soil  here  and  repotted  on  the  17th  in  sealed  containers  without  dis¬ 
turbing  the  root  system.  Pinto  beans  were  first  grown  in  pots  in  the  same 
way,  and  then  placed  in  sealed  containers  at  the  montane  station  on  the 
morning  of  June  17  and  at  the  plains  station  during  the  afternoon  of  the 
same  day.  After  the  usual  soaking,  wheat  and  oats  were  planted  directly 
in  sealed  containers  at  the  former  on  June  15.  At  the  same  time  an  equal 
number  were  planted  in  small  pots,  from  which  they  were  transferred  to 
containers  at  the  plains  station  on  June  18,  when  only  a  few  plants  had 
appeared  above  ground. 

Owing  to  losses,  caused  chiefly  by  grasshoppers,  the  original  number  of 
plants,  6  at  each  station,  was  carried  through  the  series  only  in  the  case  of 
beans.  The  sunflowers  were  reduced  to  9  (4  plains  and  5  montane),  the 
oats  to  7,  of  which  2  were  plains  and  5  montane,  and  the  wheat  to  3,  one 
plains  and  2  montane.  Soil  samples  taken  in  duplicate  gave  the  following 
holards  for  the  various  species  and  stations:  plains  station,  wheat,  oats, 
and  sunflowers  25.9  per  cent  and  beans  24.7  per  cent;  montane  station, 
wheat  and  oats  23  per  cent,  sunflowers  22.6,  and  beans  25.2  per  cent,  indi¬ 
cating  that  the  water-supply  was  essentially  identical  for  all. 

Readings. 

The  average  transpiration  per  unit  of  leaf-area  was  much  larger  for  the 
plains  than  for  the  montane  station.  For  the  sunflowers  the  average  water- 
loss  per  square  decimeter  of  leaf  was  376  c.  c.  and  264  c.  c.  respectively, 
while  for  beans  it  was  408  c.  c.  and  238  c.  c.  Stated  in  percentages,  tran¬ 
spiration  at  the  montane  station  was  70  per  cent  of  that  at  the  plains  in  the 
case  of  sunflowers  and  58  per  cent  in  the  case  of  beans.  The  individual 
variation  of  the  sunflowers  was  small,  being  but  5  per  cent  for  the  plains 
and  7  per  cent  for  the  montane  plants.  There  was  no  effective  difference 
in  leaf-area  between  the  two  stations  (table  9). 

The  plants  of  this  series  were  cut  July  10,  and  the  dry  weights  obtained 
by  drying  to  a  constant  weight  at  100°  C.  The  average  dry  weight  was 
slightly  greater  at  the  montane  than  at  the  plains  station  for  sunflower  and 
beans,  while  it  was  much  higher  at  the  latter  for  oats  and  wheat  (plate  4). 


22 


SEASON  OF  1918. 


On  the  basis  of  the  plains  values  the  percentages  at  the  montane  station 
were  101  for  sunflowers,  103  for  beans,  65  for  oats,  and  91  for  wheat.  The 
water  requirement  as  defined  by  Briggs  and  Shantz,  namely,  the  amount  of 
water  used  in  the  production  of  1  gram  of  dry  material,  was  highest  at  the 
plains  station  for  all  the  species  employed.  The  average  water  requirements 
for  plains  and  for  montane  were  respectively  518  and  370  for  sunflower,  542 
and  365  for  beans,  765  and  509  for  oats,  and  766  and  657  for  wheat.  In 
comparative  terms  the  sunflowers  required  71  per  cent,  beans  67  per  cent, 
oats  66  per  cent,  and  wheat  86  per  cent  as  much  water  at  the  montane  as  at 
the  plains  station,  these  figures  agreeing  with  those  for  transpiration  above 
(table  9). 

Phytometers,  Second  Series. 

The  second  series  of  phytometers  differed  from  the  first  chiefly  in  being 
carried  through  a  longer  period  of  growth,  namely,  until  the  22d  of  July 
instead  of  the  10th.  The  method  employed  was  essentially  the  same,  except 
that  only  2  sealed  phytometers  of  each  of  the  four  species  were  used,  and 
sweet  clover  ( Melilotus  alba)  was  substituted  for  beans.  To  disclose  any 
possible  ill  effects  of  sealing,  unsealed  phytometers  were  placed  at  each 
station  and  given  the  same  treatment  as  the  sealed  ones.  In  these,  however, 
beans  replaced  sweet  clover.  Thus,  both  stations  were  provided  with  8 
sealed  phytometers,  making  2  each  of  sunflower,  wheat,  oats,  and  sweet 
clover,  while  the  plains  station  had  16  and  the  montane  15  unsealed 
phytometers. 

Readings. 

As  in  the  first  series,  the  average  transpiration  per  unit  area  was  much 
greater  at  the  plains  station,  being  practically  twice  as  much.  Thus,  for 
sunflowers  the  water-loss  was  508  c.  c.  at  the  plains  and  252  c.  c.  at  the 
montane  station,  for  oats  367  c.  c.  and  162  c.  c.,  and  for  wheat  386  c.  c.  and 
197  c.  c.  respectively.  The  transpiration  at  the  montane  station  was  50 
per  cent  of  that  on  the  plains  for  sunflowers,  44  per  cent  for  oats,  and  51  per 
cent  for  wheat.  The  individual  variation  was  again  low  for  the  sunflowers, 
being  1  and  6  per  cent,  but  it  was  much  higher  for  the  cereals.  The  leaf- 
area  of  both  sunflowers  and  wheat  was  greater  for  the  montane  region.  The 
sunflowers  in  unsealed  containers  showed  a  much  smaller  leaf-area  at  both 
stations  than  those  in  sealed  containers,  indicating  that  sealing  did  not 
affect  growth  unfavorably.  The  relations  with  respect  to  the  average  dry 
weight  were  the  reverse  of  those  for  the  first  series,  the  values  being  higher 
at  the  plains  station  for  sunflower  and  sweet  clover,  and  higher  at  the 
montane  for  oats  and  wheat.  On  the  basis  of  the  plains  results,  the  per¬ 
centages  at  the  montane  station  were  81  for  sunflowers,  62  for  sweet  clover, 
166  for  oats,  and  230  for  wheat  (tables  9  to  12).  The  water  requirement 
was  again  higher  at  the  plains  station,  for  the  sunflowers  being  382  as 
against  285  for  the  montane  station,  for  oats  536  to  335,  for  wheat  486  to 
320,  and  for  sweet  clover  529  to  300.  The  requirement  at  the  latter  was  74 
per  cent  for  sunflowers,  63  per  cent  for  oats,  66  per  cent  for  wheat,  and  57 
per  cent  for  sweet  clover  of  that  at  the  plains  station,  agreeing  closely  with 
the  figures  for  the  first  series,  except  in  the  case  of  wheat.  It  is  somewhat 


SECOND  AND  THIRD  SERIES. 


23 


surprising  to  find  that  the  water  requirement  is  less  than  in  the  first  series, 
in  which  the  plants  were  cut  12  days  earlier. 

Phytometers,  Third  Series. 

Three  species  were  employed  as  phytometers  in  this  series,  namely,  sun¬ 
flower,  oats,  and  wild  raspberry  ( Rubus  strigosus).  While  the  methods  of 
planting  and  sealing  were  the  same,  the  soil  was  a  mixture  of  that  previously 
used  with  one-fourth  as  much  fine  gravel.  The  holard  was  18  per  cent  in 
all  cases.  Two  or  three  sealed  phytometers  were  carried  through  the  series 
at  the  five  stations,  and  unsealed  checks  of  sunflower  and  oats  were  also 
located  at  each.  All  of  these  were  installed  July  10  and  removed  August  16. 

Readings. 

The  average  transpiration  for  all  three  species  was  greatest  at  the  plains 
station  with  970  c.  c.  for  sunflower,  and  it  decreased  through  the  stations 
with  the  following  order  and  values:  gravel-slide  320,  montane  310,  spruce 
169,  and  fir  142.  In  the  case  of  oats  the  values  were  respectively  510,  390, 
335,  69,  and  28,  and  for  raspberry  401,  249,  230,  97,  and  65.  On  the  basis 
of  the  plains  station  the  water-loss  of  sunflowers  was,  respectively,  33,  32, 
17,  and  15  per  cent,  of  oats  76,  66,  14,  and  6  per  cent,  and  of  raspberries 
62,  57,  24,  and  16  per  cent.  As  to  leaf-areas,  these  were  greatest  for  oats 
and  raspberries  in  the  plains  and  least  at  the  Engelmann-spruce  and 
Douglas-fir  stations,  while  the  sunflowers  gave  the  greatest  area  in  the 
montane  and  gravel-slide  stations  for  the  sealed  phytometers,  the  results 
in  the  unsealed  ones  diverging  somewhat  (tables  9  and  12). 

The  average  dry  weight  of  sunflowers  was  greatest  at  the  montane  sta¬ 
tion,  2.5  gm.,  less  at  the  gravel-slide  and  plains  stations,  1.9  and  1.6  gm., 
respectively,  and  least  at  the  spruce  and  fir  stations,  0.36  and  0.31  gm.  As 
percentages  based  on  the  plains  station  the  values  were  152  per  cent  for  the 
montane,  118  for  the  gravel-slide,  22  for  the  spruce,  and  19  for  the  fir,  while 
for  the  unsealed  checks  they  were  respectively  93,  48,  9,  and  7  per  cent.  In 
the  case  of  oats,  on  the  other  hand,  the  relation  of  sealed  and  unsealed 
phytometers  was  reversed.  For  the  sealed  ones  the  results  were  82  per  cent 
for  the  montane,  62  for  the  gravel-slide,  20  for  the  spruce,  and  13  for  the 
fir,  while  the  unsealed  yielded,  respectively,  132, 117,  55,  and  42  per  cent. 

As  in  the  other  series,  the  water  requirements  were  highest  at  the  plains 
station  and  decreased  with  altitude  and  shade.  For  the  sunflowers  the 
averages  were  as  follows:  plains  1,140  c.  c.,  gravel-slide  489  c.  c.,  montane 
372  c.  c.,  fir  321  c.  c.,  and  spruce  316  c.  c.,  while  the  oats  gave  893,  575,  535, 
156,  and  320  c.  c.,  respectively.  Expressed  in  per  cent  of  the  plains  values, 
the  figures  are  43,  33,  28,  and  27  for  sunflower,  and  64,  60,  17,  and  36  for 
oats  (tables  9  to  12). 

Summary. 

The  results  of  the  three  series  are  summarized  in  tables  10  and  12,  and 
from  these  the  following  conclusions  may  be  drawn: 

1.  The  water  requirement  of  sunflowers  is  greater  at  the  plains  than  at 
the  montane  station.  The  order  of  decreasing  value  when  other  stations 
were  represented  is  plains,  gravel-slide,  montane,  fir,  and  spruce.  The  same 


24 


SEASON  OF  1918. 


relation  is  true  of  beans,  wheat,  and  sweet  clover  where  these  were  used,  and 
also  for  oats,  except  that  the  fir  and  spruce  stations  are  reversed. 

2.  Essentially  the  same  sequence  holds  for  the  transpiration  per  unit  of 
leaf-area,  both  for  the  cultivated  species  and  the  native  Rubus,  as  for  water 
requirement. 

3.  The  relation  shown  by  water  requirement  and  transpiration  is  similar 
to  that  found  for  temperature  and  for  the  evaporation  from  the  porous-cup 
atmometer. 

4.  In  regard  to  growth  the  response  was  less  uniform,  as  shown  both  by 
dry  weight  and  leaf-area.  Sunflowers  and  beans  usually  made  the  best 
growth  at  the  montane  station,  but  in  the  longer  second  series  the  sun¬ 
flowers  were  larger  at  the  plains  station.  In  the  case  of  the  other  species 
the  individuals  at  the  plains  were  usually  somewhat  larger,  though  the 
second  series  furnished  an  outstanding  exception  in  favor  of  the  montane 
habitat.  The  discrepancies  are  probably  to  be  explained  by  differences  in 
the  total  requirements  of  the  species  and  by  diverging  changes  in  the  factor- 
complex  with  the  advancing  season. 

5.  The  comparison  of  behavior  and  growth  in  sealed  and  unsealed  con¬ 
tainers  shows  that  presence  of  the  seal  had  no  unfavorable  effect. 


METHODS  AND  RESULTS,  SEASON  OF  1919. 

Three  climax  stations  were  maintained  during  the  season,  the  plains  and 
montane  stations  being  continued  as  for  1918.  The  third  one  was  estab¬ 
lished  in  the  subalpine  climax  of  Engelmann  spruce  ( Picea  engelmanni )  at 
an  altitude  of  10,800  feet.  It  was  located  on  the  top  of  a  ridge  along  the 
east  slope  of  Pike’s  Peak,  formed  by  the  terminal  moraine  of  an  old  glacier. 
The  ground  sloped  about  7°  to  the  northeast  and  was  strewn  with  large 
boulders.  The  spruce  trees  are  small  and  scattered  in  an  old  burn,  their 
size  being  partly  due  to  the  proximity  of  timber-line,  which  is  but  a  few 
hundred  feet  higher  at  this  point.  The  burn  is  now  largely  covered  with 
grove-like  communities  of  aspen.  The  experimental  area  was  fenced  with 
wire  screen  in  the  manner  already  described.  Owing  to  the  open  nature  of 
the  community,  it  was  unnecessary  to  effect  a  clearing  in  order  to  expose 
the  phytometers  to  the  sun  (plate  3a). 

The  detailed  methods  were  essentially  the  same  as  those  employed  in 
1918.  The  containers  used  for  both  series  were  of  sheet-metal,  and  were 
approximately  16  cm.  wide  and  20  cm.  deep.  The  soil  was  practically 
identical  with  that  used  in  the  previous  year,  being  taken  from  the  same 
spot  and  treated  in  the  same  fashion.  The  seed  was  obtained  from  the 
same  source  as  before,  and  was  germinated  and  the  plants  transferred, 
sealed,  and  cared  for  as  already  described.  The  treatment  of  the  containers 
differed  only  in  the  fact  that  no  collars  were  used,  the  soil  being  in  contact 
with  the  pails  and  thus  necessitating  careful  wiping  and  drying  before  they 
were  weighed. 

Hygro-thermographs  were  installed  in  standard  shelters  at  the  plains  and 
montane  stations,  the  readings  being  checked  each  week  by  standard  ther¬ 
mometer  and  psychrometer.  Owing  to  various  vicissitudes  it  proved  impos¬ 
sible  to  place  one  of  these  instruments  at  the  subalpine  station,  but  a 
thermograph  was  added  later,  and  psychrometer  readings  were  taken  from 
time  to  time.  Standardized  porous-cup  atmometers  were  run  in  duplicate 
at  each  station  inside  the  phytometer  inclosure,  the  cups  being  set  at  the 
approximate  level  of  the  leaves.  The  results  in  all  cases  have  been  cor¬ 
rected  to  the  standard  and  the  average  of  the  two  readings  used.  The 
rainfall  was  recorded  for  each  station,  and  the  holard  was  determined  to  a 
depth  of  3  feet  each  week  and  to  4  feet  at  the  plains  station  at  least  once  a 
month. 

Temperature. 

The  air-temperature  decreased  with  the  altitude  as  for  the  previous  year, 
but  this  fact  was  somewhat  obscured  by  the  greater  effect  of  cold-air 
drainage.  However,  the  difference  in  the  day  average  for  the  plains  and 
montane  was  much  less,  owing  to  several  inversions,  in  spite  of  the  fact  that 
the  curves  (fig.  3)  show  the  plains  to  be  usually  about  5°  higher.  Since 
the  average  for  the  plains  at  night  is  actually  lower,  there  is  indicated  no 
efficient  difference  in  the  24-hour  average  for  the  two  stations.  The  usual 
relation  is  much  more  clearly  revealed  by  the  temperatures  of  the  subalpine 
station  where  the  results  are  not  disturbed  by  the  effect  of  air  drainage. 
For  all  three  periods  they  are  10°  to  12°  higher  than  for  the  montane  region, 

25 


26 


SEASON  OF  1919. 


as  instrumental  studies  had  shown  two  decades  earlier.  The  plains  exhibit 
a  somewhat  greater  daily  range,  being  warmer  by  day  and  cooler  at  night 
than  the  montane  region. 


Humidity  and  Evaporation. 

The  relative  humidity  at  the  montane  station  was  10  per  cent  higher  than 
at  the  plains  station  for  the  summer  average  during  the  day,  while  the 
night  humidity  was  17  per  cent  lower.  The  latter  was  partly  due  to  cold- 
air  drainage,  but  chiefly,  it  would  seem,  to  two  weeks  of  unusually  high 
humidity  on  the  plains.  Since  the  day  humidity  is  several  to  many  times 
more  efficient  than  night  humidity  in  controlling  transpiration,  owing  to 
stomatal  behavior,  the  plains  are  really  drier  in  effect,  in  spite  of  the  fact 
that  the  24-hour  average  for  the  montane  region  is  3  per  cent  lower.  This 
is  also  attested  by  the  greater  evaporation  (fig.  4). 


Fig.  3. — Average  temperature  for  day  (heavy  lines),  24-hours  (medium 
lines),  and  night  (light  lines),  1919. 


Evaporation  was  highest  at  the  plains,  intermediate  at  the  montane,  and 
lowest  at  the  subalpine  station,  the  daily  averages  for  the  season  being 
respectively  32,  30,  and  20  c.  c.  The  curves  for  the  season  (fig.  5)  show 
that  the  plains  evaporation  is  often  much  higher  than  for  the  montane  zone, 
while  that  for  the  subalpine  zone  is  regularly  much  lower. 


Summary. 

For  the  season  of  1919,  the  plains  station  exhibited  the  highest  and  most 
variable  average  air-temperature,  the  highest  average  soil-temperature  and 
holard,  a  slightly  higher  relative  humidity,  and  the  highest  evaporation. 
The  montane  station  was  intermediate  in  average  air  and  soil  temperature 
and  evaporation,  slightly  lower  in  relative  humidity,  and  lowest  in  holard. 
The  subalpine  station  gave  the  lowest  and  least  variable  average  air-tern- 


FIRST  SERIES. 


27 


perature,  lowest  soil-temperature  and  evaporation,  and  an  intermediate 
holard. 


Fig.  4. — Average  humidity  for  day  (heavy  lines),  24-hours  (medium  lines),  and 

night  (light  lines),  1919. 


Phytometers,  First  Series. 

Four  species  were  employed  in  this  series,  namely,  sunflower,  pinto  beans, 
Marquis  spring  wheat,  and  Kherson  oats.  Five  sealed  and  an  equal  num¬ 
ber  of  unsealed  phytometers  were  maintained  at  each  of  the  three  stations. 
All  these  were  planted  between  June  24  and  27,  the  grains  after  a  few  days’ 
growth  in  germinators  and  the  others  after  the  expansion  of  the  cotyledons. 
Both  sunflower  and  beans  were  planted  in  flats  and  grown  in  the  greenhouse 


28 


SEASON  OF  1919. 


from  June  16  until  they  were  transferred  to  the  containers.  The  holard  of 
the  soil  varied  from  18.5  to  22  per  cent.  All  plants  were  removed  on 
August  1,  blue-prints  were  made  of  the  leaves,  and  the  green  and  dry  weights 
were  obtained  in  the  usual  manner. 


Plains - Montane  - Subalpme 


Fig.  o. — Average  evaporation,  1919. 

Readings. 

Transpiration  per  unit  of  leaf-area  agreed  with  the  results  of  the  pre¬ 
ceding  year,  being  greatest  at  the  plains  station  and  decreasing  rapidly 
with  the  altitude.  This  is  well  illustrated  by  the  sunflower,  in  which  the 
transpiration  fell  about  200  c.  c.  for  each  station,  namely,  from  644  c.  c.  to 
425  c.  c.  and  230  c.  c.  The  sunflowers  gave  65  per  cent  at  the  montane 
station  and  35  per  cent  at  the  subalpine  of  the  water-loss  at  the  plains, 
while  for  wheat  the  values  were  58  and  20  per  cent,  for  oats  44  and  37  per 


SECOND  SERIES. 


29 


cent,  and  for  beans  58  and  56  per  cent.  The  response  as  to  leaf-area  appears 
to  have  been  influenced  by  the  heat  requirements  of  the  species,  since  the 
leaves  of  sunflower  and  bean  were  largest  at  the  plains  station,  and  those 
of  wheat  and  oats  at  the  montane.  Moreover,  the  area  at  the  subalpine 
station  was  less  than  half  for  sunflower  and  less  than  a  seventh  for  beans 
of  that  at  the  plains,  while  for  both  wheat  and  oats  it  was  greater,  being 
only  a  little  less  than  in  the  montane  zone  (table  13). 

The  growth  of  the  plants,  as  indicated  by  the  dry  weight,  is  in  complete 
accord  with  the  results  for  leaf-area,  though  the  figures  are  even  more 
striking.  The  dry  weight  of  sunflower  and  bean  was  greatest  at  the  plains, 
and  that  of  wheat  and  oats  in  the  montane  region.  For  the  first  two  it 
was  reduced  approximately  50  per  cent  for  each  station,  being  12  gm.  at  the 
plains  and  3  gm.  at  the  subalpine  station  for  the  sunflower,  and  5.8  gm. 
and  0.8  gm.  respectively  for  the  bean.  For  wheat,  the  montane  value  was 
2.57  gm.,  the  subalpine  1.76  gm.,  and  the  plains  1.60  gm.,  while  for  oats  the 
respective  figures  were  1.72, 1.63,  and  1.25.  The  green  weights  are  in  general 
agreement  with  the  dry  weights,  the  ratio  between  the  two  indicating  that 
the  plants  became  more  succulent  with  increasing  altitude,  a  fact  already 
established  by  observation. 

As  established  by  the  1918  series,  water  requirement  decreased  with  the 
altitude.  For  sunflower  and  beans  the  respective  values  were  401  and  665, 
352  and  424,  and  280  and  287 ;  for  wheat  and  oats,  557  and  567,  351  and  342, 
and  173  and  249.  On  the  basis  of  the  plains  requirement,  sunflower  needed 
87  per  cent  as  much  water  in  the  montane  climax  and  72  per  cent  in  the 
subalpine,  while  wheat  required  68  and  26  per  cent  respectively.  The  rela¬ 
tive  requirement  was  much  the  same  for  oats  and  beans  in  the  montane 
region,  namely,  59  and  63  per  cent,  as  it  was  likewise  for  the  subalpine  zone, 
43  and  47  per  cent.  Thus,  while  all  species  decreased  their  requirement  with 
increasing  altitude,  sunflower  made  the  least  reduction  and  wheat  the 
greatest.  The  general  correspondence  in  the  water  requirements  of  the  four 
species  at  the  montane  station  is  significant  of  its  intermediate  position 
between  the  limiting  effect  of  heat  and  dryness  on  the  plains  and  cold  in 
the  subalpine  climax. 

Phytometers,  Second  Series. 

Three  sealed  and  three  unsealed  phytometers  of  each  of  the  three  species, 
sunflower,  Marquis  spring  wheat,  and  Kherson  oats,  were  employed  at  the 
various  stations  for  this  series.  An  accident  at  the  plains  station  left  but 
two  sunflower  and  two  wheat  phytometers  there.  In  addition  to  these,  two 
wheat  phytometers,  sealed  by  the  method  used  in  1918,  were  run  at  each 
station,  as  well  as  three  unsealed  ones  of  each  species  as  checks.  Three 
additional  checks  were  grown  in  soil  placed  in  trenches  alongside  the  regular 
containers  to  determine  the  effect  of  the  limited  size  of  the  containers  on 
the  plants  grown  in  them.  Results  for  these  are  not  included  in  the  tables, 
since  they  gave  practically  the  same  green  and  dry  weights  as  the  plants 
in  containers.  It  appears  certain  from  this  and  other  tests  that  the  con¬ 
tainers  exerted  no  limiting  effect  on  growth  for  the  relatively  short  period 
of  each  series. 


30 


SEASON  OF  1919. 


Readings. 

Transpiration  again  decreased  with  the  altitude  in  the  case  of  both 
sealed  and  unsealed  containers,  with  the  exception  of  the  sealed  wheat 
checks  at  the  plains  and  the  sealed  oats  at  the  subalpine  station.  It 
decreased  more  rapidly  with  sunflower  than  with  wheat  or  oats,  and  more 
rapidly  with  the  unsealed  than  the  sealed  phytometers.  The  average  water 
requirement  showed  a  constant  decrease  from  the  plains  to  the  montane  and 
subalpine  stations,  with  the  exception  of  oats  at  the  second,  where  the  high 
value  results  in  an  inexplicable  discrepancy.  The  results  as  to  growth  in 
terms  of  leaf-area  and  dry  weight  vary  so  much  from  those  obtained  in 
preceding  series  as  to  indicate  an  exceptional  irregularity  in  the  conditions 
of  growth  for  the  different  species  at  the  various  stations  (tables  13  and  14). 

Summary. 

1.  Transpiration  decreased  with  the  altitude  in  both  series,  being  greatest 
on  the  plains  and  least  in  the  subalpine  zone. 

2.  Water  requirement  likewise  decreased  with  the  altitude  in  both  series. 

3.  Growth  was  regularly  best  for  temperate  species,  sunflower  and  beans, 
at  the  plains  station,  while  for  boreal  ones,  wheat  and  oats,  it  was  usually 
best  at  the  montane  station. 


METHODS  AND  RESULTS,  SEASON  OF  1920. 

The  same  three  stations,  plains,  montane,  and  subalpine,  were  main¬ 
tained  in  1920  as  for  the  previous  season,  no  alterations  that  could  effect 
conditions  being  made.  Three  species  were  used  through  the  season,  during 
which  two  series  of  phytometers  were  run,  comprising  sunflowers,  Marquis 
spring  wheat,  and  Kherson  oats.  The  seed  was  obtained  from  the  same 
source  as  that  used  in  former  years  and  was  as  nearly  as  possible  identical 
with  it.  Soil,  containers,  methods  of  handling  the  plants,  and  sealing  were 
precisely  the  same  as  described  for  the  second  series  of  1919.  Five  sealed 
and  five  unsealed  plants  of  each  species  were  installed  at  each  station.  In 
addition  to  these,  three  phytometers  in  large  containers  4.5  dm.  deep  by  3 
dm.  in  diameter  were  planted  with  wheat  at  both  the  plains  and  montane 
stations,  two  of  each  battery  being  sealed  in  the  same  way  as  the  smaller 
containers,  while  the  third  was  left  unsealed  as  a  check.  The  results  for 
these  large  containers  are  given  at  the  end  of  the  other  phytometer  data, 
as  they  were  run  in  but  one  series. 


Fig.  6. — Average  temperature  for  day  (heavy  lines),  24-hours  (medium  lines), 

and  night  (light  lines),  1920. 


Hygro-thermographs  were  operated  at  each  station  in  standard  shelters 
placed  on  the  ground  close  to  the  experimental  inclosures.  The  instru¬ 
ments  were  checked  weekly  by  duplicate  thermometer  and  psychrometer 
readings.  In  case  of  an  error  of  5  per  cent  or  more,  as  occasionally 
happened  with  the  hydrograph,  the  averages  given  in  the  table  were 
obtained  by  integration.  Standardized  white  cylindrical  atmometers  with 
non-absorbing  mounts  were  run  in  duplicate  within  each  inclosure  and  so 
placed  as  to  bring  the  evaporating  surface  as  nearly  level  with  the  leaves 
as  possible.  As  in  the  case  of  those  for  the  previous  season,  the  results  are 
averages  based  on  weekly  readings  of  the  two  instruments.  An  anemometer 
was  placed  in  each  inclosure  and  the  cups  brought  to  a  height  of  12  inches 
above  the  surface  of  the  ground  to  get  as  nearly  as  possible  the  conditions 
of  wind  to  which  the  leaves  were  exposed.  Rain  was  recorded  at  each 
station,  and  the  holard  at  various  depths  was  determined  weekly. 

31 


32 


SEASON  OF  1920. 


Temperature. 

In  average  temperature  for  the  season,  the  plains  station  is  highest,  the 
montane  second,  and  the  subalpine  lowest,  the  averages  for  the  season 


•Plains 


Montane 


-Subalpine 


Fig.  7. — Average  rainfall,  24-hour  humidity,  total  wind,  and 

average  evaporation,  1920. 

being  respectively  64.5°,  59.1°,  and  50.5°  (fig.  6).  The  curves  of  the  24- 
hour  averages  for  the  period  show  plainly  a  relation  through  the  summer 
similar  to  that  indicated  by  the  summer  averages.  There  is  a  close  agree- 


PHYSICAL  FACTORS. 


33 


ment  between  the  variations  in  temperature  at  the  three  stations,  especially 
during  the  first  part  of  the  season,  corresponding  with  the  first  series  of 
phytometers,  while  during  the  second  series  the  subalpine  temperatures 
show  a  decline,  indicating  the  early  approach  of  autumn  at  the  higher 
altitudes.  The  averages  yield  the  same  relation,  viz,  plains  stations  65.4° 
and  63.7°,  montane  station  58.3°  and  59.9°,  and  subalpine  station  51.3° 
and  49.7°  for  the  first  and  second  series  respectively.  The  day  averages 
for  the  plains  station  are  relatively  high.  Thus,  the  results  for  the  time 
of  the  first  series  show  a  difference  between  the  day  average  at  the  plains 
(73.2°)  and  at  subalpine  stations  (56.6°)  of  16.6°,  while  the  differences 
between  the  24-hour  averages  is  14.1°.  For  the  second  series,  the  differences 
were  15.5  and  14°  respectively.  The  night  averages  for  the  two  stations 
naturally  show  less  difference  than  the  24-hour  averages,  viz,  11.7°  and 
12.3°,  for  the  respective  periods.  Thus,  the  temperature  for  the  season 
varies  inversely  with  the  altitude  of  the  stations,  being  highest  at  the  plains, 
especially  during  the  day,  and  lowest  at  the  subalpine  station,  particularly 
at  night.  The  plains  station  showed  the  greatest  difference  between  day  and 
night  temperatures  and  the  subalpine  the  least. 

Holard  and  Humidity. 

In  total  rainfall  for  the  season  of  1920  the  plains  station  was  lowest  with 
8.13  inches,  the  montane  second  with  10.74  inches,  the  subalpine  highest 
with  12.13  inches.  From  the  weekly  rainfall  at  the  three  stations  (fig.  7), 
it  will  be  seen  that  the  last  part  of  the  summer  received  more  rain  than 
the  first,  the  maximum  at  all  stations  being  reached  during  the  week  of 
August  16.  It  is  also  evident  that,  while  the  average  at  the  subalpine 
station  exceeded  that  at  the  montane,  the  rainfall  at  the  latter  was  often 
greater.  The  rain-gages  were  kept  in  close  proximity  to  the  phytometers 
and  read  weekly,  an  oil  seal  being  used  to  reduce  evaporation.  The  holard 
exhibited  no  constant  difference  between  the  stations,  though  in  general  the 
surface  layers  of  the  soil  at  the  plains  and  the  montane  stations  gave  higher 
readings  than  at  the  subalpine,  while  the  deeper  layers  at  the  latter  were 
in  general  moister. 

In  average  relative  humidity,  the  subalpine  station  was  high,  the  plains 
second,  and  the  montane  low,  the  averages  for  the  season  being  62.5,  62.3, 
and  59.3  per  cent,  respectively.  The  daily  24-hour  averages  are  graphed 
in  figure  7,  which  shows  plainly  the  general  rise  of  humidity  during  the 
latter  part  of  the  summer.  This  same  relation  of  the  humidity  is  shown 
by  comparing  the  24-hour  average  for  the  period  of  the  first  and  second 
series.  These  averages  are  57.7  and  66.9  per  cent  for  the  plains  station, 
55.3  and  63.3  for  the  montane,  and  60.4  and  70.6  per  cent  for  the  subalpine 
station  in  the  first  and  second  series  respectively. 

In  comparing  the  stations  on  the  basis  of  the  day  and  the  night 
humidities,  the  order  is  changed,  the  average  day  humidities  for  the  season 
being  plains  49.4  per  cent,  montane  51.9  per  cent,  and  subalpine  64.5  per 
cent,  while  the  corresponding  average  night  values  are  77,  68.6  and  71.6  per 
cent.  The  plains  station  thus  shows  the  lowest  day  humidity  but  the 
highest  night  average.  This  may  be  expressed  in  the  form  of  the  difference 


34 


SEASON  OF  1920. 


between  the  night  and  day  values  and  gives  27.6  per  cent  for  the  plains, 

16.7  per  cent  for  the  montane,  and  7.1  per  cent  for  subalpine  station.  This 
variation  between  night  and  day  humidity  was  somewhat  less  during  the 
second  series  at  the  plains  and  montane  stations,  but  greater  at  the  sub- 
alpine  station,  the  differences  for  the  plains  station  being  30.2  and  25  per 
cent,  montane  18.8  and  14.5  per  cent,  and  subalpine  station  3.3  and  10.9 
per  cent  for  the  first  and  second  series  respectively.  Thus,  the  average 
relative  humidity  for  the  24  hours  of  the  day  is  slightly  the  highest  at  the 
subalpine,  second  at  the  plains,  and  lowest  at  the  montane  station,  the  daily 
variation  being  greatest  at  the  plains  and  least  at  the  subalpine  station.  The 
night  humidity  averages  highest  at  the  plains  and  lowest  at  the  montane 
station,  but  the  subalpine  station  yielded  the  highest  day  humidity  and  the 
plains  station  the  lowest. 

Evaporation. 

In  general,  evaporation  was  highest  at  the  plains,  second  at  the  montane, 
and  lowest  at  subalpine  station,  the  weekly  averages  for  the  season  being 
respectively  25.8  c.  c.,  19.0  c.  c.  and  17.2  c.  c.  During  most  of  the  season 
the  evaporation  at  the  plains  station  was  markedly  above  that  of  either  of 
the  others  (fig.  7),  while  for  the  latter  part  of  the  summer,  corresponding 
in  time  to  the  second  series,  the  results  are  lower  than  for  the  first  series. 
This  reduction  in  evaporation  during  the  latter  part  of  the  season  is  also 
shown  by  comparing  the  averages  for  the  first  series  with  those  of  the 
second  series,  the  values  being  plains  28.5  c.  c.  and  23.5  c.  c.,  montane 

21.7  c.  c.  and  14.5  c.  c.,  and  subalpine  station  21.4  c.  c.  and  13.3  c.  c.  The 
atmometers  used  were  run  in  duplicate  within  the  screen  inclosure  of  each 
station,  the  evaporating  surface  being  set  at  approximately  the  level  of  the 
leaves  of  the  phytometer  plants.  The  values  recorded  were  averages  from 
the  standardized  readings  of  the  two  instruments. 

Wind. 

The  average  weekly  wind  movement  was  greatest  at  the  plains,  second  at 
the  subalpine,  and  least  at  the  montane  station,  the  values  being  respectively 
366.7,  215.1,  and  204.7  miles.  The  weekly  average  for  the  first  series  is 
greater  at  the  plains  and  subalpine  stations,  but  less  at  the  montane  station 
than  for  the  second  series.  The  graph  of  the  weekly  totals  shows  the  com¬ 
paratively  high  and  variable  values  at  the  plains  station  (fig.  7).  While 
the  wind  at  the  subalpine  was  above  that  at  the  montane  station  during 
the  earlier  part  of  the  season,  it  dropped  slightly  below  the  latter  through 
most  of  the  late  summer  period.  The  anemometers  in  all  cases  were  located 
within  the  screen  inclosures  on  a  level  approximating  that  of  the  leaves. 

Summary. 

For  the  period  observed,  the  plains  station  showed  the  highest  and  most 
fluctuating  temperatures,  especially  during  the  day,  the  lowest  rainfall,  a 
moderately  high  surface  holard,  the  lowest  relative  humidity  during  the 
day,  but  the  highest  during  the  night,  the  greatest  total  amount  of  wind, 
and  the  highest  average  evaporation.  The  subalpine  station  showed  the 


FIRST  SERIES. 


35 


lowest  and  most  constant  temperature,  the  greatest  rainfall,  a  relatively 
low  holard  in  the  surface  layers  but  high  in  the  subsoil,  the  highest  and 
most  constant  average  relative  humidity,  an  evaporation  which  at  times 
exceeded  and  at  times  fell  below  that  at  the  montane  station,  and  a  total 
number  of  miles  of  wind,  which,  for  the  season,  slightly  exceeded  that  at 
the  montane  station,  but  was  little  over  one-half  that  at  the  plains  station. 
The  montane  station  was,  in  general,  intermediate,  but  on  the  whole 
approached  conditions  at  the  subalpine  more  closely  than  those  at  the  plains 
station. 

The  second  series  of  phytometers  was  operated  under  conditions  of  tem¬ 
perature  similar  to  those  of  the  first  series,  except  at  the  subalpine  station, 
where  the  early  approach  of  autumn  reduced  the  average  somewhat,  but 
under  conditions  of  greater  humidity,  much  greater  rainfall,  less  wind,  except 
at  the  montane  station,  and  less  evaporation. 

By  a  comparison  of  the  physical  factors  for  1919  and  1920,  it  is  evident 
that  the  1920  phytometers  were  grown  under  conditions  of  lower  tempera¬ 
ture,  greater  rainfall,  higher  holard,  greater  relative  humidity,  and  less 
evaporation. 

Phytometers,  First  Series. 

Each  battery  consisted  of  5  sealed  and  5  unsealed  phytometers  of  each 
species,  1  plant  being  used  in  each  sunflower  phytometer  and  5  plants  in 
each  wheat  or  oats  phytometer.  The  sunflower  seeds  were  soaked  and 
planted  June  5  and  those  of  the  grains  June  6.  When  the  plants  were  well 
started,  they  were  transferred  to  containers  filled  with  soil  taken  from  the 
same  spot  as  in  the  previous  series.  The  containers  were  the  same  as  those 
used  in  the  second  series  of  1919  and  were  filled  and  sealed  in  the  same  way, 
i.  e.,  by  the  method  of  the  wax-cloth  seal.  All  phytometers  were  started 
at  the  plains  station  June  11,  at  the  montane  station  June  13,  and  at  the 
subalpine  station  June  12.  They  were  weighed  at  all  stations  June  14  and 
this  weight  was  taken  as  initial. 

At  the  time  of  weighing  and  watering  each  week,  three  measurements 
were  made  of  each  sunflower,  viz,  the  height  of  stem,  stem  diameter  1  cm. 
above  the  surface  of  the  seal,  and  the  extreme  length  and  width  of  each 
cotyledon  or  leaf-blade.  For  the  grains,  the  measurements  consisted  merely 
of  the  extreme  width  and  length  of  each  blade,  measurements  of  length 
being  taken  from  the  ligule,  and  the  number  of  stems  per  container.  To  get 
as  accurate  an  estimate  as  possible  of  the  weekly  leaf-area  from  these 
measurements,  about  300  sunflower  leaves  of  various  sizes  and  taken 
from  various  parts  of  plants  grown  from  the  same  lot  of  seed  as  that  used 
for  the  phytometers  were  measured  under  conditions  similar  to  those  in  the 
experimental  areas.  They  were  then  removed  from  the  plant  and  blue¬ 
prints  made,  the  areas  of  the  latter  being  obtained  later  by  duplicate  read¬ 
ings  with  a  planimeter.  The  leaf-areas  in  square  centimeters  thus  obtained 
were  compared  with  the  product  of  the  leaf  dimensions  measured  in  milli¬ 
meters  and  the  average  factor  found  that  would  give  the  area  of  both  sides 
of  the  leaf  from  the  product  of  its  dimensions.  This  method  was  applied 
to  sunflower  leaves  and  cotyledons  as  well  as  to  the  leaves  of  the  grains. 
For  the  sunflower  leaves  it  was  found  that  the  area  of  both  sides  of  the  leaf 


36 


SEASON  OF  1920. 


in  square  centimeters  is  obtained  by  dividing  the  product  of  the  leaf 
dimensions  in  millimeters  by  79,  thus  giving  a  factor  of  approximately 
0.013.  In  practice,  the  area  of  the  sunflower  leaves  in  square  centimeters 
was  found  from  the  product  of  the  extreme  dimensions  in  millimeters,  by 
multiplying  by  0.013.  Results  obtained  by  a  similar  method  gave  for 
sunflower  cotyledons  the  factor  0.016  and  for  grain  leaves  0.015.  To  make 
sure  of  the  applicability  of  this  factor  to  leaves  grown  in  the  field,  it  was 


- - Plains - Montane - Subalpine 

Fig.  8. — Average  leaf-area  and  transpiration  of  sunflowers, 

first  series,  1920. 


carefully  checked  against  leaf-areas  obtained  by  the  planimeter  from  blue¬ 
prints  made  from  the  leaves  of  field-grown  plants.  In  case  a  part  of  the 
leaf  was  lost  through  accident,  the  area  of  the  destroyed  portion  was  care¬ 
fully  estimated  and  subtracted  from  the  area  of  the  leaf  as  computed  by 
the  above  method.  All  leaves  which  appeared  withered  were  removed  and 
filed  in  envelopes  under  the  number  of  the  phytometer  from  which  they 
came,  so  that  the  entire  dry  weight  could  be  found  at  the  end  of  the  series. 

On  July  19  all  plants  were  cut  at  the  surface  of  the  seal  after  the  above 
measurements  had  been  made,  and  the  green  weight  of  the  plant-tops  grown 


TRANSPIRATION. 


37 


in  each  phytometer  was  obtained.  The  plants  were  then  brought  to  the 
laboratory  and  a  few  of  the  leaves  removed  and  blue-prints  made,  in  order 
to  check  the  factor  used  in  obtaining  the  area  against  any  possible  variation 
in  leaf-shape  due  to  the  peculiar  conditions  at  the  various  stations.  The 
plant  material  taken  from  each  phytometer  was  cut  into  small  pieces,  dried 
in  an  oven,  cooled  in  a  desiccator,  and  weighed. 

Transpiration. 

The  transpiration  per  unit  leaf-area  varied  in  general  inversely  with 
the  altitude,  being  greatest  at  the  plains  and  least  at  the  subalpine  station. 
In  weekly  water-loss  per  square  decimeter  of  leaf-area  (fig.  8),  there  is  a 
rather  close  correlation  between  the  curves  for  the  plains  and  for  the  sub¬ 
alpine  sunflowers,  the  transpiration  for  the  week  of  July  12  being  the  only 


- Plains - Montane  - Subalpine 

Fig.  9. — Average  stem-length  (heavy  lines)  and  diameter  (light 
lines)  of  sunflowers,  first  series,  1920. 


one  for  which  the  rates  do  not  agree.  On  the  other  hand  (figs.  10  and  11), 
there  is  a  better  correlation  between  the  transpiration  of  wheat  and  oats 
at  the  montane  and  subalpine  stations  than  between  the  plains  and  either 
of  the  others.  The  great  decline  in  the  transpiration-rate  of  plains  wheat 
and  oats  during  the  third  week  of  the  series  is  surprising,  since  it  coincided 
with  an  increase  in  average  daily  evaporation  and  total  weekly  wind,  but 
harmonizes  with  the  beginning  of  a  decline  in  the  rate  of  leaf-growth  for 
these  two  plants,  though  not  for  the  sunflowers  growing  under  the  same 
conditions.  Evidently,  the  conditions  which  became  operative  at  the  plains 
station  the  week  ending  July  5  caused  a  slight  reduction  in  the  rate  of 
leaf-growth  and  in  the  transpiration  per  unit  leaf-area  of  wheat  and  oats, 
but  permitted  a  slight  increase  in  the  transpiration  of  the  sunflowers  and  had 
no  noticeable  effect  on  the  rate  of  leaf  expansion.  At  the  same  time  that 
the  grains  at  the  plains  station  fell  from  a  high  to  a  low  rate,  the  plants  at 
the  montane  and  subalpine  stations  agreed  in  starting  from  a  low  rate  of 
water-loss  and  rising  to  a  comparatively  high  one.  Since  there  was  an 


38 


SEASON  OF  1920. 


increase  in  rainfall  at  all  the  stations,  and  since  the  sunflowers  were  not 
affected,  it  seems  that  the  factors  operative  in  reducing  the  leaf-growth  and 
water-loss  for  the  plains  wheat  and  oats  were  physiological  rather  than 
physical. 

To  facilitate  comparison  between  the  average  transpiration  per  unit  leaf- 
area  for  the  various  plants  and  the  factor  readings,  the  transpiration  curves 
have  been  plotted,  together  with  those  of  average  temperature,  average 
relative  humidity,  average  daily  evaporation,  and  total  weekly  wind  (figs. 
12,  13,  14).  In  figure  12  the  sunflower  transpiration  curve  is  roughly  the 
reciprocal  of  all  the  instrumental  curves  and  is  a  particularly  good  recip¬ 
rocal  of  those  for  relative  humidity  and  evaporation.  At  the  plains  station 


Fig.  10. — Average  leaf-area  (heavy  lines)  and  transpiration 
(light  lines)  of  wheat,  first  series,  1920. 

the  transpiration  of  the  sunflowers  was  apparently  affected  by  factors  other 
than  those  in  control  of  evaporation  from  the  atmometer  cups.  At  the 
montane  station,  however,  the  transpiration  curve,  while  the  reciprocal  of 
the  humidity  curve  as  for  the  plains  station,  shows  close  correlation  with 
the  temperature  curve  and  also  with  the  curve  of  average  evaporation. 
Evidently  in  this  case  temperature  and  evaporation  are  good  indexes  of  the 
transpiration  of  these  leaves,  and  probably  temperature  was  the  controlling 
factor  for  both  transpiration  and  evaporation.  In  the  curves  from  the 
subalpine  station,  while  there  is  no  close  correlation,  there  is  a  general  one 
with  evaporation,  temperature,  and  relative  humidity.  Thus,  transpiration 
per  unit  leaf-area  in  the  sunflowers  regularly  gives  a  correlation  with 
average  temperature,  average  relative  humidity,  average  evaporation,  and 
total  wind,  though  the  behavior  at  the  plains  station  was  more  or  less 
exceptional. 

The  transpiration  of  the  plains  wheat  (fig.  13)  is  not  correlated  closely 
with  any  instrumental  curve,  but  shows  the  best  relation  to  the  curve  of 
average  relative  humidity.  There  is  a  general  correlation  with  all  the 


TRANSPIRATION. 


39 


instrumental  curves,  but  the  transpiration  of  the  plains  wheat  varied  in  a 
manner  the  reverse  of  that  of  the  sunflowers  under  the  same  conditions. 
The  transpiration  of  the  montane  wheat  shows  a  positive  correlation  with 
the  curves  of  average  temperature  and  average  relative  humidity.  The 
subalpine  curves  are  compared  in  figure  13.  This  shows  again,  as  in  figure 
12  for  the  sunflowers,  a  negative  correlation  of  the  transpiration  with 
average  relative  humidity  and  a  positive  correlation  between  the  tran¬ 
spiration  and  the  average  temperature  and  evaporation  curves.  The 
transpiration  of  wheat  varied  in  general  with  average  temperature,  average 
relative  humidity,  average  evaporation,  and  total  wind  at  the  plains  station, 
with  average  temperature  and  evaporation  and  inversely  with  average 


Fig.  11. — Average  leaf-area  (heavy  lines)  and  transpiration 
(light  lines)  of  oats,  first  series,  1920. 

relative  humidity  at  the  montane  station,  and  with  average  temperature  and 
evaporation  and  inversely  with  average  relative  humidity  at  the  subalpine 
station. 

There  is  a  general  correlation  of  the  transpiration  of  the  plains  oats  with 
average  temperature,  average  evaporation,  average  relative  humidity,  and 
total  wind  (fig.  14).  Assuming  that  the  transpiration  results  for  the  first 
week  might  have  been  abnormal  because  of  the  recent  transplanting  and 
sealing  of  the  plants,  the  closest  correlation  is  with  the  curve  of  average 
temperature.  The  transpiration  of  oats  in  the  montane  zone  shows  a  rather 
close  correlation  with  average  temperature,  evaporation,  and  average 
relative  humidity.  The  same  relation  is,  in  general,  true  for  the  results 
from  oats  at  the  subalpine  station.  The  transpiration  per  unit  leaf-area  of 
the  oats  varied  directly  at  all  the  stations,  as  did  the  wheat,  with  average 
temperature  and  evaporation,  and  inversely  with  the  average  relative 


40 


SEASON  OF  1920. 


Sunflower - Evaporation - 

- Temperature - Wind 


Humidity 


Fig.  12. — Average  transpiration  of  sunflowers 
and  physical  factors,  first  series  1920 
(humidity  curves  inverted) :  plains  (be¬ 
low),  montane  (middle),  subalpine 
(above). 


Wheat - Evaporation - Humidity 

- Temperature - Wind 


Fig.  13. — Average  transpiration  of  wheat, 
and  physical  factors,  first  series,  1920 
(humidity  curves  inverted) :  plains  (be¬ 
low),  montane  (middle),  subalpine 
(above). 


GROWTH. 


41 


humidity  at  the  montane  and  subalpine  stations.  The  frequent  dis¬ 
crepancies  in  the  agreement  of  the  curves  indicate  the  importance  of 
physiological  as  well  as  physical  conditions. 

Growth. 

The  weekly  increase  in  leaf-area  of  the  sunflowers  was  highest  at  the 
plains,  second  at  the  montane,  and  lowest  at  the  subalpine  station  (fig.  8). 
The  leaf-area  began  high  at  the  plains  station  because  the  plants  were  first 
installed  there  and  hence  recovered  from  the  shock  of  transplanting  before 
those  at  the  upper  stations,  but  the  increased  rate  of  growth  of  the  mon¬ 
tane  plants  brought  the  leaf-area  to  a  point  approximately  equal  to  that 
of  the  plains  phytometers.  In  contrast  to  this,  the  subalpine  sunflowers 
maintained  a  comparatively  slow  rate  of  growth  and  showed  little  accel¬ 
eration  during  the  time  of  this  series.  As  to  leaf-area  of  wheat  and  oats 
(figs.  10  and  11),  the  relation  of  the  stations  is  markedly  different.  Both 
showed  a  similar  initial  rate  of  leaf-expansion  at  all  stations,  but  after  the 
third  week  of  the  series  the  rate  of  growth  at  the  plains  station  fell  off  so 
rapidly  that  by  the  end  of  the  experiment  the  leaf-area  at  the  plains  station 
was  exceeded  by  that  at  both  the  montane  and  subalpine  stations.  Begin¬ 
ning  with  the  week  of  June  28  to  July  5,  there  was  a  marked  increase  in 
evaporation  at  the  plains  station  over  that  at  the  other  stations,  a  fact 
perhaps  explained  by  the  simultaneous  rise  in  wind,  since  there  was  little 
change  in  average  temperature  and  an  actual  increase  in  rainfall  and 
average  relative  humidity.  The  behavior  of  the  cereals  at  the  subalpine 
station  was  also  strikingly  different  from  that  of  the  sunflowers.  Instead 
of  maintaining  a  more  or  less  constant  rate  of  growth  to  the  end  of  the 
series,  wheat  and  oats  agree  in  showing  a  great  acceleration  in  rate  of  leaf- 
expansion  throughout  the  period  of  the  experiment. 

Increase  in  stem-length  for  the  sunflower  followed  the  leaf-growth 
closely  (fig.  9).  After  the  first  two  weeks,  during  which  recovery  from 
transplanting  took  place  most  rapidly  at  the  plains  station,  and  least  so  at 
the  subalpine,  the  rate  of  stem-elongation  continued  about  the  same  at  the 
plains  and  montane  stations  throughout  the  series,  but  was  much  less  at 
the  subalpine  one.  Unlike  the  rate  of  leaf-growth,  the  rate  of  stem- 
elongation  at  the  montane  did  not  exceed  the  rate  at  the  plains  station. 
However,  the  rate  of  increase  in  the  diameter  of  the  stems  at  the  plains 
was  never  equal  after  the  second  week  to  that  at  the  montane  station  and 
in  fact  barely  exceeded  that  at  the  subalpine  one.  All  stem  diameters  were 
measured  by  means  of  a  vernier  caliper  reading  in  millimeters  and  tenths, 
while  the  stem-length  was  taken  by  a  ruler,  the  measurement  being  the 
distance  from  the  surface  of  the  seal  to  the  base  of  the  terminal  bud. 

Dry  Weight. 

With  respect  to  green  and  dry  weights,  plants  at  the  plains  station  gave 
the  highest  figures,  those  of  the  montane  next,  and  those  at  subalpine 
lowest.  This  is  in  agreement  with  the  leaf-area  of  the  sunflowers,  but  not 
with  the  size  of  the  cereals  as  indicated  by  their  leaf-area  (figs.  10  and  11). 
Thus,  the  wheat  and  oats  showed  a  final  leaf-area  greater  at  the  montane 


42 


SEASON  OF  1920. 


- Oats - Evaporation - Humidity 

- . Temperature - Wind 

Fig.  14. — Average  transpiration  of  oats,  and 
physical  factors  (humidity  curves  in¬ 
verted):  plains  (below),  montane 
(middle),  subalpine  (above). 


and  subalpine  stations  than  at  the  plains 
station,  but  a  greater  dry  weight  at  the 
latter  than  at  either  of  the  upper  loca¬ 
tions.  This  difference  in  the  growth  of 
the  plants  at  the  various  elevations  is 
shown  more  clearly  by  the  percentage 
relation  between  green  weight  and  dry 
weight.  This  percentage  decreases  with 
the  increasing  altitude  of  the  stations  at 
which  the  phytometer  plants  w^ere  grown. 
Expressed  in  other  words,  the  plants 
showed  increasing  succulence  with  the 
increasing  altitude  of  the  stations  where 


- Plains - Montane  - Subalpine 

Fig.  15. — Average  leaf-area  and  transpiration  of  sun 
flowers,  second  series,  1920. 


SUMMARY  OF  FIRST  SERIES. 


43 


they  developed.  The  data  for  unsealed  check  phytometers  shows  that, 
measured  by  either  green  or  dry  weight,  these  were  not  consistently  larger 
than  the  sealed  phytometers.  The  percentages  correspond  in  general  with 
those  already  given  for  the  sealed  plants. 

Water  Requirement. 

The  water  requirements  of  the  plants  in  this  series  are  similar  to  those 
obtained  in  the  earlier  part  of  this  work  in  that  they  were  greatest  at  the 
plains  station.  They  differ  from  preceding  results  in  being  more  nearly 
equal  for  all  the  stations,  and  also  in  the  fact  that  sunflower  and  wheat 
gave  values  at  the  montane  station  lower  than  those  for  the  subalpine.  The 
water  requirements  for  sunflowers  were  456.3,  415.07,  and  434.29,  for  wheat 
650.99,  530.7,  and  543.35,  and  for  oats  543.35,  532.41,  and  520.96  at  the 
plains,  montane,  and  subalpine  stations  respectively  (fig.  24) .  These  values 
are  in  general  below  those  obtained  for  the  plants  of  the  second  series  of 
1919,  and  this  is  likewise  true  when  the  comparison  is  made  with  the 
sunflowers  of  the  first  series  of  1919. 

Summary. 

On  the  whole,  transpiration  per  unit  leaf-area  was  greatest  at  the  plains 
station,  less  at  the  montane,  and  least  at  the  subalpine  for  all  species.  The 
transpiration  rates  of  the  grains  were  in  fairly  close  agreement,  but  differed 
materially  from  that  of  the  sunflower.  The  transpiration  of  the  sunflowers 
showed  no  positive  correlation  with  any  instrumental  curve  at  the  plains 
station,  but  was  correlated  negatively,  in  a  general  way,  with  all.  At  the 
montane  and  subalpine  stations,  however,  the  sunflower  transpiration  cor¬ 
related  positively  with  the  average  temperature  and  evaporation  curves 
and  negatively  with  the  curve  of  average  relative  humidity.  The  tran¬ 
spiration  of  wheat  and  oats  showed  a  general  positive  correlation  with  all 
instrumental  curves  at  the  plains  station  and  with  average  temperature  and 
evaporation  at  the  montane  ■  and  subalpine  stations  and  a  negative  cor¬ 
relation  with  average  relative  humidity  at  the  montane  and  subalpine 
stations.  As  a  criterion  of  transpiration,  evaporation  as  measured  by  the 
white  cylindrical  atmometers  showed  no  greater  correlation  than  other 
factors,  such  as  temperature. 

For  sunflower,  the  smallest  growth  occurred  at  the  subalpine  station  in 
leaf-area,  stem-length,  and  stem-diameter.  The  greatest  stem  elongation 
took  place  on  the  plains,  but  the  greatest  increase  in  stem-diameter  in  the 
montane  zone.  The  initial  rate  of  leaf-expansion  for  the  sunflower  was 
greatest  at  the  plains  station,  but  was  exceeded  by  the  rate  at  the  montane 
station  during  the  latter  half  of  the  series,  the  sunflowers  finally  showing  the 
greatest  leaf-area  and  stem-length  on  the  plains,  but  the  greatest  diameter 
at  the  montane  station. 

Wheat  and  oats  agreed  in  showing  the  most  rapid  leaf-expansion  on  the 
plains  for  the  first  part  of  the  series,  but  a  marked  decrease  in  the  growth- 
rate  occurred  after  the  third  week,  so  that  the  final  leaf-area  of  the  cereals 
was  less  at  the  plains  station  than  at  the  others. 

In  size,  as  measured  by  both  dry  and  green  weight,  the  three  species  were 
largest  at  the  plains,  second  at  the  montane,  and  smallest  at  the  subalpine 


44 


SEASON  OF  1920. 


station.  In  view  of  the  fact  that  the  final  leaf-area  of  the  plains  and  mon¬ 
tane  sunflowers  was  approximately  equal  and  of  the  wheat  and  oats  was 
greater  at  the  montane  than  at  the  plains,  it  is  evident  that  the  montane 
plants  had  more  leaf-surface  in  proportion  to  their  mass  than  the  plants  on 
the  plains. 

The  percentage  relation  of  dry  weight  to  green  weight  decreased  with 
the  increasing  altitude  of  the  stations  at  which  the  plants  were  grown. 

No  marked  dwarfing  effects  due  to  sealing  were  evident. 

The  water  requirement,  while  slightly  largest  at  the  plains  station  for 
all  three  species,  was  on  the  whole  not  less  at  the  subalpine  than  at  the 
montane  station.  For  sunflower  and  oats  the  difference  was  so  small  as  to 
be  within  the  limits  of  error,  but  wheat  gave  a  value  materially  higher  for 
the  plains  station. 

During  the  first  series  the  sunflowers  at  the  plains  station  attained 
greater  height,  slightly  greater  leaf-area,  and  greater  dry  and  green  weight 
with  less  proportional  water  in  the  tissue  than  at  any  other  station,  but 
were  second  to  the  montane  sunflowers  in  stem-diameter.  The  water 
requirements  of  sunflower  and  oats  were  hardly  greater  at  the  plains  than 
at  the  other  stations,  but  the  value  for  wheat  at  the  former  was  considerably 
above  that  at  the  other  two  stations.  All  the  plants  showed  a  greater  suc¬ 
culence  when  grown  at  increased  altitudes,  and  likewise  agreed  in  producing 
more  leaf-surface  in  proportion  to  their  green  and  dry  weight  at  the  montane 
than  at  the  other  stations. 


Second  Series. 

For  the  second  series  the  same  methods  were  employed  as  for  the  first, 
the  kinds  and  numbers  of  plants,  stations,  containers,  and  soil  being 
identical.  The  sunflower  achenes  were  soaked  and  planted  in  flats  July  14; 
they  were  transplanted  to  the  containers  and  sealed  at  the  various  stations 
on  July  21  to  23.  The  seeds  of  the  cereals  were  soaked  and  placed  in 
germinators  July  19  and  planted  in  the  containers  on  the  same  dates. 
These  containers  were  not  immediately  sealed  and  weighed,  however,  as 
the  wheat  and  oats  seedlings  made  poor  initial  growth.  The  holard  found 
in  the  containers  was:  plains  15.25,  montane  14.8,  and  subalpine  station 
16.9  per  cent.  The  plants  were  removed  August  30,  bringing  the  series  to  a 
close.  The  only  obvious  difference  from  the  first  series  was  the  poor  growth 
of  the  wheat  at  the  plains  station,  making  replanting  necessary  the  second 
week  of  the  series. 


Transpiration. 

In  general,  the  transpiration  per  unit  leaf-area,  as  in  the  first  series, 
varied  inversely  with  the  altitude  of  the  stations.  The  transpiration  curves 
for  the  sunflowers  at  the  various  stations,  unlike  those  of  the  first  series, 
exhibit  a  fairly  close  correlation  (fig.  15).  However,  wheat  at  the  plains 
station  gave  a  low  transpiration-rate,  falling  below  the  montane  station 
for  all  but  the  final  week  of  the  series  (fig.  17),  but  this  is  not  surprising 
in  view  of  its  poor  growth.  The  curves  of  transpiration  for  montane  and 
subalpine  wheat  are  closely  correlated,  neither  showing  much  increase  until 


SECOND  SERIES. 


45 


the  final  week  of  the  series.  The  transpiration  of  oats  (fig.  18),  while 
giving  rather  poor  correlation  between  the  stations,  agrees  rather  closely 
with  the  sunflower  values  at  the  montane  station,  but  not  elsewhere. 

The  transpiration  of  the  plains  sunflowers  shows  no  close  positive  cor¬ 
relation  with  any  instrumental  curve.  There  is  a  negative  correlation  with 
the  curve  of  average  relative  humidity  (fig.  19),  but  the  average  tem¬ 
perature  is  quite  as  good  a  measure  of  transpiration  as  evaporation,  neither 


- Plains - Montane  - Subalpine 

Fig.  16. — Average  stem  length  and  diameter  of  sunflowers,  second 

series,  1920. 


agreeing  with  the  transpiration  curve.  The  transpiration  of  the  montane 
sunflowers  shows  much  the  same  result  as  the  above  (fig.  19),  there  being 
a  poor  negative  correlation  of  the  transpiration  curve  with  that  of  relative 
humidity  and  an  equally  poor  positive  correlation  with  the  temperature  and 
evaporation  curves.  The  transpiration  of  the  subalpine  sunflowers  gives 
an  even  poorer  correlation  with  the  physical  factors  for  that  station.  There 
is  a  negative  correlation  with  the  relative  humidity  curve  and  a  rough 
positive  correlation  with  the  curves  of  temperature  and  evaporation.  The 
transpiration  of  the  sunflowers  showed  a  negative  correlation  with  the 


46 


SEASON  OF  1920. 


average  relative  humidity,  but  no  close  positive  correlation  with  any 
instrumental  readings  made. 

Plains  wheat  exhibits  a  fairly  close  positive  correlation  between  tran¬ 
spiration,  temperature,  and  wind,  but  no  correlation  between  the  tran¬ 
spiration  curve  and  that  of  evaporation  or  humidity  (fig.  20).  Montane 
wheat  gives  a  positive  correlation  between  transpiration,  evaporation,  and 
temperature,  but  no  consistent  variation  with  wind  or  relative  humidity. 
At  the  subalpine  station  the  relations  are  similar  in  that  there  is  no  close 
correlation  between  the  curve  of  transpiration  and  that  of  any  of  the  instru¬ 
mental  results. 


-  Plains  - - — Montane - Subalpine 

Fig.  17. — Average  leaf-area  and  transpiration  of  wheat,  second 

series,  1920. 


The  transpiration  of  the  plains  oats  shows  a  close  positive  correlation 
with  the  evaporation  and  a  fair  negative  correlation  with  average  relative 
humidity  (fig.  21).  At  the  montane  station  the  transpiration  curve  also 
exhibits  a  general  agreement  with  the  curve  of  average  evaporation  and  a 
rough  negative  correlation  with  the  relative  humidity  curve.  The  results 
for  the  subalpine  oats  show  a  close  positive  correlation  between  the  wind 
and  the  transpiration,  as  well  as  a  general  positive  correlation  between  the 
transpiration  and  evaporation  curves. 

The  transpiration  values  for  the  second  series  thus  show  that  roughly 
the  sunflowers  varied  at  the  plains  station  directly  with  evaporation  and 
inversely  with  relative  humidity,  at  the  montane  station  directly  with 
evaporation  and  temperature  and  inversely  with  relative  humidity,  and 


GROWTH. 


47 


at  subalpine  station  directly  with  evaporation,  temperature,  and  wind  and 
inversely  with  relative  humidity.  Wheat  at  the  plains  station  agreed 
directly  with  evaporation,  temperature,  and  wind,  at  the  montane  station 
directly  with  evaporation,  and  at  the  subalpine  station  directly  with  tem¬ 
perature.  Oats  varied  at  the  plains  and  montane  stations  directly  with 


Fig.  18. — Average  leaf-area  and  transpiration  of  oats,  second 

series,  1920. 


evaporation  and  inversely  with  relative  humidity,  and  at  the  subalpine  one 
directly  with  wind  and  evaporation.  The  correlations  were  more  or  less 
imperfect  in  nearly  all  cases. 

Growth. 

The  weekly  leaf-areas  were  highest  at  the  plains  station  in  every  case. 
Leaf-growth  at  the  montane  station  was  greatest  from  the  beginning,  but 
the  rate  at  the  plains  and  subalpine  stations  did  not  vary  greatly  until 
after  the  fourth  week,  the  greatest  difference  occurring  the  last  week. 


48 


SEASON  OF  1920. 


Thus,  on  August  23  the  area  of  the  subalpine  sunflowers  was  6.17  sq.  dm. 
and  on  August  30,  6.26  sq.  dm.,  while  the  area  of  the  plains  sunflowers  was 
7.8  and  12.83  sq.  dm.  respectively.  On  the  same  dates  the  montane  sun- 


Fig.  19. — Average  transpiration  of  sunflowers, 
and  physical  factors,  second  series,  1920 
(humidity  curves  inverted) :  plains  (below), 
montane  (middle),  subalpine  (above). 


- Wheat - Evaporation - Humidity 

~ - -Temperature - Wind 

Fig.  20. — Average  transpiration  of  wheat,  and 
physical  factors,  second  series,  1920 
(humidity  curves  inverted):  plains  (below), 
montane  (middle),  subalpine  (above). 


DRY  WEIGHT  AND  WATER  REQUIREMENT. 


49 


flowers  yielded  areas  of  17.91  and  23.51  sq.  dm.,  or  about  twice  that  of  the 
plains  plants  (fig.  15).  The  leaf-area  of  the  wheat  was  very  low  for  the 
plains  station  (fig.  17),  the  plants  at  the  montane  and  subalpine  stations 
being  very  much  larger.  This  is  explained  by  the  fact  that  the  wheat 
seedlings  on  the  plains  did  not  recover  from  transplanting  and  were  replaced 
the  second  week  of  the  series.  The  phytometers  at  the  montane  and  plains 
stations  gave  similar  weekly  increases,  the  rate  of  leaf-expansion  diverging 
markedly  only  during  the  last  week,  when  the  rate  of  the  montane  plants 
exceeded  that  for  the  subalpine  station.  The  oats  gave  a  rate  of  leaf- 
growth  more  like  that  of  the  sunflower  than  of  the  wheat  (fig.  18).  As  in 
the  sunflowers,  the  final  area  of  the  montane  oats  was  greatest,  but  the 
plains  oats,  in  spite  of  their  late  start,  soon  attained  approximately  the 
same  leaf-area  as  those  at  the  montane  station  and  maintained  a  similar 
rate  to  the  end.  The  subalpine  oats  showed  a  low  rate  of  growth  and  a 
small  leaf-area  throughout  the  series. 

As  to  leaf-area,  the  montane  station  yielded  in  general  the  highest  values 
for  all  plants.  The  plains  oats,  however,  gave  an  area  approximately  equal 
to  that  of  the  montane  plants.  The  plains  sunflowers,  while  somewhat 
larger  than  the  subalpine  ones,  were  far  smaller  than  the  montane.  The 
plains  wheat  had  the  smallest  leaf-area  of  the  series,  while  the  subalpine 
station  exhibited  the  lowest  leaf-area  for  oats  and  sunflowers,  but  produced 
wheat  with  a  leaf-area  almost  equal  to  that  of  the  montane  plants.  In 
average  stem  elongation  the  sunflowers  at  the  plains  and  montane  stations 
gave  similar  values  (fig.  16),  the  main  difference  being  the  increased  rate 
of  the  former  during  the  final  week  of  the  series,  an  increase  which  raised 
the  average  considerably  above  that  for  the  montane  group.  In  stem- 
length  the  subalpine  sunflowers  were  far  below  those  at  the  other  stations 
while  the  stem-diameter  was  greatest  at  the  montane  station.  The  plains- 
station  values  remained  low,  never  even  exceeding  those  from  the  subalpine 
station  plants.  The  subalpine  sunflowers  were  small  both  as  to  stem-length 
and  diameter,  while  montane  sunflowers  were  largest  in  both  stem-length 
and  diameter  during  the  first  part  of  this  series,  but  were  exceeded  in  stem- 
length  by  the  plains  sunflowers  during  the  last  week  of  the  experiment. 

Dry  Weight  and  Water  Requirement. 

As  measured  by  the  green  weight  of  the  tops,  the  sunflowers  and  wheat 
made  the  best  growth  at  the  montane  station,  but  the  oats  made  a  slightly 
better  growth  at  the  plains  than  at  the  other  stations.  The  percentage 
relation  between  dry  weight  and  green  weight  shows  that  the  sunflowers 
display  the  same  relation  as  that  already  discussed  for  the  preceding  series, 
viz,  the  percentage  decreases  with  the  increasing  altitude  of  the  stations  at 
which  the  plants  were  grown.  For  the  cereals,  on  the  other  hand,  the 
relation  is  reversed,  i.  e.,  the  percentage  increases  with  increasing  altitude. 
For  the  wheat  this  is  not  so  surprising  when  one  recalls  that  the  plains 
plants  made  such  poor  growth  as  to  necessitate  replanting  and  hence  were 
younger  and  more  succulent  than  the  plants  at  the  other  stations.  The  size 
of  the  plants  as  indicated  by  the  dry  weights  corresponds  to  the  relation 
discussed  under  leaf-area,  viz,  the  sunflowers  and  wheat  were  largest  at  the 


50 


SEASON  OF  1920. 


montane  station,  the  sunflowers  smallest  at  the  subalpine  station,  and  the 
wheat  smallest  at  the  plains  station.  The  oats  showed  the  greatest  dry 
weight  at  the  plains  station,  second  at  the  montane  station,  and  smallest 
at  the  subalpine  station.  No 
conspicuous  dwarfing  effects  due 
to  sealing  were  evident  from  a 
comparison  of  the  green  and  dry 
weights  of  the  sealed  and  un¬ 
sealed  phytometers. 

The  water  requirement  (fig. 

24)  of  sunflower  was  similar  to 
that  obtained  in  the  first  series, 
the  plains  station  being  highest 
with  a  value  of  437.1,  the  mon¬ 
tane  lowest  with  a  value  of 
357.04,  and  the  subalpine  inter¬ 
mediate  with  that  of  396.6.  For 
wheat  and  oats,  however,  water 
requirement  was  greatest  at  the 
plains  station  in  every  case,  and 
least  at  the  subalpine,  thus  de¬ 
creasing  with  increasing  altitude, 
as  in  the  series  for  1918  and 
1919. 


Summary. 

The  transpiration  per  square 
decimeter  of  leaf-area  decreased 
from  the  plains  through  the 
montane  to  the  subalpine  climax 
as  in  the  first  series.  The  plains 
wheat,  however,  gave  a  value  be¬ 
low  that  of  the  montane  station. 
There  was  no  close  agreement 
between  the  transpiration  of 
wheat  and  oats,  contrary  to  the 
results  in  the  first  series.  At  the 
plains  station  the  transpiration 
of  sunflowers  varied  directly 
with  evaporation  and  inversely 
with  relative  humidity,  while  at 
the  other  two  stations  it  varied 
directly  with  temperature  also. 
The  transpiration  of  wheat  fluc¬ 
tuated  directly  with  temperature 
and  wind  at  the  plains  station, 
with  evaporation  and  tempera¬ 
ture  at  the  montane  station,  and 
with  temperature  at  subalpine 


Fig.  21. — Average  transpiration  of  oats,  and 
physical  factors,  second  series,  1920 
(humidity  curves  inverted):  plains  (below), 
montane  (middle),  subalpine  (above). 


LARGE  PHYTOMETERS. 


51 


station,  and  that  of  oats  varied  directly  with  evaporation  and  inversely  with 
relative  humidity  at  the  plains  and  montane  stations  and  directly  with 
evaporation  and  wind  at  the  subalpine.  The  evaporation  from  standardized, 
white,  cylindrical  atmometer  cups  gave  no  better  indication  of  the  water- 
loss  from  plants  than  other  factors,  such  as  average  temperature. 

The  sunflowers  made  the  best  growth  in  leaf-area  and  stem-diameter  at 
the  montane,  but  the  greatest  growth  in  stem-length  at  the  plains  station. 
Growth  as  measured  by  leaf-area,  stem-length,  and  stem-diameter  was 
least  at  the  subalpine  station,  but  the  difference  in  leaf-area  and  stem- 
diameter  between  this  and  the  plains  was  small.  Wheat  in  general  showed 
the  greatest  leaf-area  at  the  montane  station,  with  the  subalpine  a  close 
second.  The  leaf-area  of  the  oats  was  high  at  the  montane  and  plains 
stations  and  low  at  the  subalpine  one. 

As  measured  by  both  dry  and  green  weight,  the  sunflowers  were  largest 
at  the  montane,  second  at  the  plains,  and  third  at  the  subalpine  station ;  the 
wheat  largest  at  the  montane,  second  at  the  subalpine,  and  smallest  at  the 
plains  station;  and  oats  largest  at  the  montane,  second  at  the  plains,  and 
smallest  at  the  subalpine  station.  Since  the  final  leaf-area  of  the  oats  was 
slightly  greater  at  the  montane  than  at  the  plains  station,  and  the  dry  and 
green  weights  showed  the  reverse  relation,  the  oats  plainly  agree  with  those 
of  the  first  series  in  showing  a  greater  leaf-area  in  proportion  to  their  weight 
at  the  montane  than  at  the  plains  station.  The  other  plants,  however,  do 
not  show  this  relation.  The  percentage  relation  of  dry  weight  to  green 
weight  decreases  with  the  increasing  altitude  of  the  stations  for  the  sun¬ 
flowers,  although  the  unsealed  checks  show  a  slightly  greater  value  for  the 
subalpine  than  for  the  montane  station.  Relations  for  the  wheat  and  oats 
are,  in  general,  the  reverse  of  this,  although  the  wheat  checks  show  little 
difference  between  the  stations  and  the  oats  have  the  highest  value  at  the 
montane  station. 

The  water  requirement,  as  defined  by  Briggs  and  Shantz,  was  greatest  in 
every  case  at  the  plains  station;  it  was  least  at  the  montane  station  for  sun¬ 
flowers,  but  at  the  subalpine  for  wheat  and  oats,  in  accordance  with  their 
boreal  character. 

During  the  second  series  the  sunflowers  grew  to  a  greater  height  at  the 
plains  station,  but  gave  a  greater  stem-diameter,  leaf-area,  and  green  and 
dry  weight  at  the  montane  station.  The  water  requirement  was  greatest  at 
the  plains  station,  decreasing  with  increasing  altitude  for  wheat  and  oats, 
but  was  smallest  at  the  montane  station  for  the  sunflowers.  The  values  for 
the  leaf-area  proportional  to  the  weight  and  for  the  succulence  of  the  plants 
vary  in  the  different  cases. 


Large  Phytometers. 

Since  large  containers  are  difficult  to  handle  as  well  as  expensive  to 
install  in  the  mountains,  the  smaller  containers,  described  in  connection 
with  the  1919  series,  were  used  in  the  greater  part  of  this  investigation. 
While  there  seemed  no  good  reason  to  doubt  the  validity  of  results  obtained 
from  small  containers  when  the  results  were  secured  before  the  roots  became 
crowded,  it  was  thought  desirable  to  use  larger  containers  to  check  this. 


52 


SEASON  OF  1920. 


Batteries  of  sunflower  phytometers  in  galvanized-iron  containers,  45  cm. 
deep  by  30  cm.  in  diameter,  were  established  at  the  plains  and  montane 
stations  in  1919,  but  the  accidental  destruction  of  the  plants  precluded 
obtaining  results  of  value.  In  1920  a  battery  of  three  wheat  phytometers, 
two  sealed  and  one  unsealed  check,  was  installed  at  the  plains  and  also  at 
the  montane  station  at  the  same  time  and  under  the  same  conditions  of 
soil,  and  with  the  same  methods  as  those  employed  for  the  smaller  con¬ 
tainers.  It  was  hoped  that  the  results  would  indicate  whether  the  6-weeks 
period  was  too  long  for  dependable  results  from  the  latter.  The  size  of 
the  phytometers  necessarily  made  the  method  of  weighing  less  accurate  than 
that  employed  for  the  small  containers.  At  the  time  of  watering,  each  con¬ 
tainer  was  removed  from  the  soil,  wiped  dry,  and  weighed  carefully  by 
means  of  a  pair  of  steelyards  weighing  to  4  ounces,  water  being  added  to 
restore  the  original  weight,  as  in  the  case  of  the  smaller  cans  (plate  3b)  . 


- Large  containers 

- First  series 'wheat 

Fig.  22. — Average  transpiration  of  large 
phytometers  and  wheat,  first  series,  1920. 

Wheat  was  substituted  for  the  sunflowers  used  in  1919,  because  the  great 
water-loss  from  the  latter  made  more  frequent  watering  necessary.  How¬ 
ever,  this  choice  was  unfortunate,  as  the  season  at  the  plains  station  proved 
to  be  unsuited  for  the  good  development  of  wheat.  The  destruction  of 
some  of  the  plants  by  grasshoppers  was  the  climax  of  misfortune  at  that 
station  and  left  the  data  from  the  montane  station  as  the  only  trustworthy 
results  available  for  comparison  with  those  obtained  by  the  use  of  the 
small  containers.  Nevertheless,  the  lack  of  complete  results  from  the  plains 
does  not  greatly  impair  the  value  of  the  data  from  the  montane  station 
for  purposes  of  comparison  (fig.  22). 


GENERAL  SUMMARY,  1918-1920. 


53 


The  transpiration  per  square  decimeter  of  leaf-area  for  the  large  phyto¬ 
meters  is  plotted  in  figure  22,  together  with  the  results  from  the  montane 
wheat  for  the  first  series,  this  series  being  used  because  the  plants  were 
handled  in  identically  the  same  way  as  those  of  the  large  phytometers, 
except  for  the  differences  involved  in  the  size  of  the  container.  As  the  large 
phytometers  were  carried  through  the  season,  this  curve  extends  to  August 
30.  It  will  be  seen  that  there  is  a  general  decline  in  the  curve  with  the 
advance  of  the  season  and  the  age  of  the  plants.  Except  for  the  com- 


Fig.  23. — Average  transpiration  of  large  phytometers,  1920,  compared  with 

factor  data. 


paratively  high  value  for  the  week,  June  28  to  July  5,  the  transpiration 
rate  of  the  montane  wheat  corresponds  well  with  that  of  the  wheat  in  the 
larger  containers,  the  average  transpiration  for  the  five  weeks  being  84.3  c.  c. 
for  the  former  and  84.2  c.  c.  for  the  latter. 

A  comparison  of  the  weekly  leaf-areas  shows  no  indication  of  abnormal 
growth  for  the  wheat  in  the  small  containers  (figs.  10  and  17),  and  this  is 
essentially  true  also  of  the  rate  of  leaf-expansion  for  the  large  and  small 
containers. 

GENERAL  SUMMARY,  1918-1920. 

1.  The  transpiration  per  square  decimeter  of  leaf-area  was  highest  at 
the  plains,  lower  at  the  montane,  and  lowest  at  the  subalpine  station,  this 
relation  persisting  whether  the  weekly  or  the  final  area  was  used  as  a  basis. 
The  transpiration  did  not  vary  consistently  with  any  single  instrumental 
record.  No  better  correlation  obtained  between  transpiration  and  evapora¬ 
tion  from  a  white  cylindrical  atmometer  cup  than  between  transpiration 
and  average  temperature. 

2.  The  leaf-area,  both  final  and  weekly,  was  usually  greatest  at  the 
montane  and  second  at  the  plains  station,  though  the  weekly  area  was 


54 


GENERAL  SUMMARY,  1918-1920. 


subject  to  great  relative  variations.  The  stem-diameter  of  sunflowers  was 
greatest  at  the  montane  and  second  at  the  plains  station,  but  the  stem- 
length  was  greatest  at  the  plains,  the  subalpine  values  for  both  diameter 
and  height  being  low. 

3.  The  size  of  plants  as  measured  by  both  green  and  dry  weights  varies 
relatively,  the  largest  plants  being  produced  at  times  at  the  montane 
station  and  at  other  times  at  the  plains  station.  In  general,  however,  plants 
with  a  high  optimum  temperature,  such  as  sunflowers,  made  the  best 


Sunflrs.  Wheat  Oats  Beans  Sunflrs.  Wheat  Wheat  Oats 


S3  Plains 


I  1  Montane  HHHH  Subalpine 


Fig.  24. — Comparative  water  requirements  of  plants  of  first  and  second  series,  1920. 


growth  at  the  plains  station  during  the  early  part  of  the  summer  and  at  the 
montane  station  during  the  late  summer,  while  plants  with  a  lower  optimum, 
such  as  wheat,  made  the  best  growth  at  the  montane  station. 

4.  The  water  requirement,  as  defined  by  Briggs  and  Shantz,  generally 
decreases  with  the  increase  in  altitude  of  the  stations  at  which  the  plants 
are  grown.  This  increase  in  growth  efficiency  with  increasing  altitude  is 
variable,  however,  and  under  some  environmental  conditions  the  relation 
may  be  reversed. 

5.  No  harmful  effects  appeared  to  result  from  sealing.  The  results  from 
phytometers  in  large  containers  indicated  that  no  abnormal  effects  ensued 
from  the  use  of  small  containers  for  the  periods  concerned. 


METHODS  AND  RESULTS,  SEASON  OF  1923. 

In  order  to  obtain  stations  in  which  the  control  was  exerted  by  a  single 
factor,  the  selection  was  made  on  the  basis  of  light  intensity.  One  station 
was  located  in  full  sunshine,  another  in  half-shade  approximately,  and  the 
third  in  dense  shade  (plates  5,  6a).  These  were  all  on  essentially  the  same 
level  and  within  100  yards  of  each  other  in  the  narrow  valley  of  Ruxton 
Brook,  which  flows  past  the  Alpine  Laboratory.  They  thus  afforded  the 
maximum  differences  in  physical  factors  consistent  with  accessibility  and 
economy  of  time  and  effort,  and  were  in  sharp  contrast  with  the  stations 
of  preceding  years,  which  were  several  miles  apart  and  in  different  climax 
zones.  The  sun  station  was  carpeted  with  grasses,  of  which  Poa  pratensis, 
Bromus  ciliatus,  B.  pumpellianus ,  and  Agropyrum  caninum  were  the  most 
important.  In  the  half-shade  station  the  cover  consisted  chiefly  of 
Thalictrum  jendleri,  Geranium  richardsoni,  Zygadenus  elegans,  and  Gen - 
tiana  amarella  beneath  a  canopy  of  Pseudotsuga  mucronata.  The  light 
intensity  of  the  full  shade  was  too  low  to  permit  the  growth  of  herbs,  except 
for  scattered  shade  forms  of  two  or  three  species.  The  instrumental 
installation  at  each  station  consisted  of  ecographs  for  recording  humidity 
and  the  temperature  of  the  air  and  soil,  and  of  anemometers  and  atmometers 
for  measuring  wind  and  evaporation  respectively.  Light  intensities  were 
determined  by  means  of  stop-watch  photometers,  and  the  sums  obtained  by 
chemical  photometers. 

FIRST  SERIES. 

Sunflower  seeds  of  the  ordinary  cultivated  variety  were  planted  on  May 
29  and  later  transplanted  from  the  flats  to  3-inch  pots  rendered  impervious 
by  closing  the  bottom  with  a  paper  disk  and  dipping  in  melted  paraffin. 
The  plants  were  then  moved  from  Colorado  Springs  to  the  Alpine  Labora¬ 
tory  and  after  2  days  for  adjustment  were  sealed  by  fitting  a  collar  of 
plastocene  modeling  clay  tightly  about  the  base  of  the  stem  and  pouring 
melted  paraffin  over  the  surface  of  the  soil.  100  plants  were  thus  sealed, 
weighed,  and  the  leaf-product  determined;  they  were  then  exposed  at  the 
sun  station  for  standardization.  During  this  period  of  a  week,  the  indi¬ 
vidual  plants  were  frequently  moved  about  in  the  inclosure  to  eliminate 
differences  arising  from  location.  At  the  close  of  the  period,  the  weight  and 
leaf-area  were  again  determined  (table  19),  and  the  individuals  selected 
for  the  respective  batteries,  plants  with  too  great  deviation  or  otherwise 
undesirable  as  phytometers  being  discarded.  While  the  plants  measured 
varied  from  23  to  65  with  respect  to  water-loss,  those  employed  were 
chosen  from  the  middle  values,  viz,  44  to  55,  and  were  grouped  in  the  three 
batteries  in  such  fashion  as  to  give  essentially  the  same  transpiration, 
namely,  47.8  for  the  sun,  47.7  for  the  half-shade,  and  47.7  for  the  full-shade 
station. 

Each  battery  consisted  of  10  plants,  which  were  placed  in  the  containers 
on  June  12,  and  sealed  and  weighed  the  next  day,  when  the  batteries  were 
placed  in  the  respective  station  inclosures.  To  each  were  added  two  con¬ 
tainers  of  the  same  type,  which  were  filled  with  soil  and  employed  as 
checks  to  test  the  efficiency  of  the  seal.  Ten  or  more  plants  of  the  same 

55 


56 


SEASON  OF  1923. 


general  value  were  planted  in  each  station  in  a  trench  filled  with  the  soil 
used  for  the  containers.  These  checks  were  designed  to  furnish  a  record  of 
growth  that  would  permit  the  recognition  of  possible  abnormal  effects  due 
to  sealing. 

Containers. 


Containers  were  made  by  soldering  a  galvanized-iron  funnel  in  the 
inverted  position  to  a  10-inch  pail  in  such  a  manner  as  to  reduce  the  opening 
to  4  inches.  The  edges  of  the  opening  were  rolled  over  a  heavy  wire,  and 
the  funnel  was  pierced  by  half-inch  tubes,  the  one  near  the  opening  extend¬ 
ing  0.25  inch  below  the  cover  and  the  one  near  the  rim  reaching  within  0.25 
inch  of  the  bottom  of  the  pail.  These  permitted  both  top  and  bottom 


Fig.  25. — Average  temperature  for  day  (heavy  lines),  24-hours  (medium  lines),  and 

night  (light  lines),  1923. 


watering  and  made  effective  aeration  possible  by  means  of  drawing  air  from 
the  longer  tube  and  allowing  it  to  enter  through  the  shorter.  The  small 
aperture  possessed  the  advantage  of  reducing  the  area  to  be  covered  by 
the  seal  and  correspondingly  diminished  the  danger  of  cracking,  while  the 
rolled  rim  afforded  a  firm  basis  for  fastening  the  cloth  of  the  seal.  The 
conical  cover  favored  filling  and  firming  the  soil  and  hence  reduced  the 
subsequent  danger  of  settling  and  cracking,  while  the  two  tubes  insured 
adequate  aeration  of  the  soil  as  well  as  uniform  distribution  of  the  water. 

The  containers  were  first  filled  to  a  depth  of  1  cm.  with  coarse  gravel  to 
serve  as  a  reservoir  and  to  permit  the  ready  movement  of  air  and  water, 
and  then  with  sifted  loam,  which  was  well  firmed  over  the  entire  surface. 
The  plants  selected  were  removed  from  the  3-inch  pots,  placed  in  the  con¬ 
tainers  with  the  least  possible  damage  to  the  roots,  and  sealed  by  means  of 
a  plastocene  collar  and  a  cover  of  wax  cloth,  as  already  described.  Paraffin 
melting  at  56°  was  used  and  proved  entirely  resistant  to  the  highest  tem¬ 
peratures  at  the  shade  and  half-shade  stations,  but  in  the  sun  it  was  found 
desirable  to  cover  it  with  a  thin  coat  of  plastocene  clay.  The  tubes  were 


FIRST  SERIES. 


57 


closed  with  rubber  stoppers  and  the  containers  sunk  in  the  ground  to  three- 
fourths  their  depth. 

The  phytometers  were  weighed  each  week,  and  the  dimensions  of  stem 
and  leaf  measured  at  the  same  time.  The  behavior  of  the  stomata  was 
determined  throughout  a  24-hour  day  at  several  times  during  the  series, 
and  the  dry  weight  and  total  sugar  found  at  the  close.  Analyses  of  the 
soil-air  in  the  containers  were  also  made  at  varying  intervals,  and  changes 
in  the  structure  of  representative  leaves  were  recorded  at  the  end  of  each 
series. 


_  Sun _ Half-shade  _ Shade 

Fig.  26. — Average  24-hour  temperature  (heavy  lines),  average  daily  wind  (medium 
line),  and  average  standard  evaporation  (light  lines),  1923.  Each  space  equals 
5  units;  the  base-line  is  0  for  evaporation  and  wind  and  25  for  temperature. 


Temperature. 

Thermographs  were  maintained  at  each  station  in  standard  shelters 
placed  on  the  ground.  The  stations  differed  less  in  air-temperature  than 
would  be  expected,  owing  largely  to  continued  cloudiness  as  well  as  to  the 
greater  radiation  in  the  sun.  While  there  was  a  constant  decrease  in 
average  temperatures  from  sun  through  half-shade  to  shade,  this  was  only 
slightly  efficient,  as  the  figures  indicate.  The  respective  day  averages  were 
63.8°,  62.8°,  and  59.8°,  the  night  averages  52.1°,  51.4°,  and  49.6°,  and  the 
24-hour  averages  57.9°,  56.8°,  and  54.6°.  Throughout  the  period  the 
averages  were  constantly  2°  to  6°  higher  at  the  half-shade  than  at  the 
shade  station;  the  relation  between  the  sun  and  half-shade  was  less  constant, 
though  the  former  was  usually  1°  to  3°  higher.  The  differences  as  well  as 


58 


SEASON  OF  1923. 


the  fluctuations  were  probably  due  in  part  to  cold-air  drainage  and  varia¬ 
tions  in  the  volume  and  temperature  of  the  brook  (fig.  25). 

The  average  weekly  soil-temperature  at  4  inches  was  constantly  about 
10°  higher  at  the  sun  than  at  the  shade  station,  the  average  difference  for 
the  series  being  9°.  This  is  to  be  ascribed  chiefly  to  insolation,  but  it  arose 
in  part  also  from  the  nearness  of  the  cold  brook  to  the  shade  station.  No 
ecograph  was  available  for  the  half-shade  station,  but  frequent  readings 
with  the  soil  thermometer  gave  intermediate  values. 

Humidity  and  Evaporation. 

The  average  day  humidity  was  practically  the  same  in  the  sun  and  half¬ 
shade,  but  it  was  6°  higher  in  the  full-shade.  On  the  contrary,  the  average 
night  humidity  at  the  sun  station  was  6°  higher  than  at  the  half-shade  and 
3°  more  than  at  the  shade  station,  thus  making  the  average  24-hour 


Sun _ _ _  Half-shade  _ Shade 


Fig.  27. — Average  transpiration  of  sunflowers,  1923. 

humidity  respectively  6°  and  2°  higher  at  the  first.  The  reduced  humidity 
in  the  sun  station  during  the  daytime  was  obviously  a  matter  of  insolation 
and  greater  wind  movement,  while  the  high  night  value  is  probably  to  be 
explained  by  the  fact  that  it  was  inclosed  on  three  sides  by  brooks,  from 
which  humid  air  drained  into  the  pocket-like  area.  The  average  daily  wind 
movement  was  greatest  in  the  sun  station,  intermediate  in  the  half-shade, 
and  least  in  the  full  shade,  the  respective  figures  being  12.3,  3.3,  and  0.99 
miles.  These  were  doubtless  wholly  the  effect  of  the  difference  in  cover. 
As  the  anemometers  were  placed  within  the  station  inclosures  and  as  near 
the  plants  as  possible,  the  results  indicate  the  actual  wind  movement 
effective  upon  the  phytometers. 


PHYSICAL  FACTORS. 


59 


As  usual,  evaporation  was  determined  by  means  of  white  cylindrical 
atmometers  of  the  porous-cup  type  exposed  in  duplicate  at  the  level  of  the 
foliage  in  each  station  inclosure.  The  average  evaporation  in  the  sun  was 
practically  twice  that  for  the  half-shade,  and  this  was  nearly  twice  that 
for  the  full-shade,  the  respective  amounts  being  18.56,  9.8,  and  5.19  c.  c. 
The  same  relation  was  maintained  throughout  the  series,  showing  that  the 
factors  for  'evaporation  were  constantly  different  for  the  three  stations 
(fig.  26). 


JUNE 

II  18  25 

JULY  AUGUST 

18  15  22  29  5  12  19  26 

\ 

— 

\ 

/  / 

A 

r 

\ 

\ 

T~ 

/ 

/ 

!  \  ■ 

/ 

x 

' 

i 

/  ^ 
/  / 

/  / 

»  \  r 

\  \ 

\  \ 
\  ' 
v 

\ 

1  /  \  - 

■ 

/  / 

/ 1 
/  / 

// 

</ 

% 

\ 

-'A' 

\ 

\  \ 
t  \ 

\  \ 

/ 

/ 

— 

-  — 

- 

-*■  ** 

r 

\ 

"  \  \ 

\\ 

\\ 

\\ 

Y 

_  -  * 

y  \ 

/ 

. « ' 

\\ 

>  •  • 

* 

V  \ 

Transpiration - Temperature - r-- - Wind 

_ Evaporation - Humidity 


Fig.  28. — Average  transpiration  of  sunflowers,  sun  station,  1923,  compared  with 
factor  data.  Each  space  equals  5  units,  except  for  the  inverted  humidity  curve, 
for  which  the  value  is  10;  the  base-line  is  0  for  transpiration,  and  wind  and 
evaporation,  and  25  for  temperature. 

Light. 

Chemical  photometers,  employing  a  solution  of  oxalic  acid  and  uranium 
acetate  in  accordance  with  the  method  of  Ridgway  (1918)  and  exposed 
against  a  uniform  background  and  at  a  uniform  angle  in  each  station,  were 
utilized  for  obtaining  light  values  at  the  three  stations  on  four  representative 
days  during  the  first  series.  The  amount  of  oxalic  acid  decomposed  during 
the  daylight  hours  was  used  as  the  basis  for  computing  the  percentage  of 
light  on  that  of  the  sun  station.  As  measured  by  this  instrument,  the  light 
intensity  in  the  half-shade  was  45  per  cent  and  in  the  full-shade  4.5  per 
cent  of  the  value  at  the  sun  station,  values  which  were  too  high,  as  shown 
by  the  stop-watch  photometers  employed  in  the  second  series. 


60 


SEASON  OF  1923. 


Transpiration. 

Water-loss  was  constantly  highest  at  the  sun  station,  and  it  was  usually 
higher  at  the  half-shade  than  at  the  full-shade  station,  in  accordance  with 
the  physical  factors  generally  (figs.  27  to  30).  The  respective  values  per 
unit  of  leaf-area  were  25,  12,  and  10.  The  correlation  of  the  transpiration 
curve  with  those  for  the  factors  concerned  or  with  that  of  evaporation  is 
nowhere  very  close,  but  the  correspondence  with  their  composite  effect  is 
fairly  good. 


- - Transpiration - - —  Temperature  - Wind 

- Evaporation - Humidity 

Fig.  29. — Average  transpiration  of  sunflowers,  half-shade  station,  1923,  compared 

with  factor  data;  values  as  in  fig.  28. 

Growth. 

As  would  be  expected  in  consequence  of  the  dense  shade,  increase  in  leaf- 
area  was  very  low  at  the  shade  station,  while  it  was  correspondingly  high 
at  the  sun  station,  the  half-shade  being  intermediate  (plate  7).  The 
respective  values  from  shade  to  sun  for  the  sealed  phytometers  were  396, 
309,  and  135  sq.  cm.  (table  17;  figs.  31  to  33).  The  converse  was  naturally 
true  of  stem-length,  the  plants  in  shade  and  half-shade  much  exceeding 
those  in  the  sun,  the  respective  heights  being  305,  428,  and  203  mm.  (fig. 
32).  Until  the  last  two  weeks  there  was  little  difference  in  the  height  of 
the  phytometers  in  the  two  shade  stations,  but  those  in  the  dense  shade 
finally  proved  too  weak  to  support  their  weight  and  some  of  the  tallest 
became  so  twisted  and  bent  that  they  were  destroyed  by  wind  and  rain 
before  the  final  readings  were  made  (plate  7).  The  average  stem-diameter 
varied  in  the  same  manner  as  the  leaf-area,  being  greatest  in  the  sun  (7.45 
mm.),  somewhat  less  in  the  half-shade  (6.64  mm.),  and  least  in  the  shade 


RESULTS. 


61 


(4.27  mm.).  Thus,  the  best  conditions  for  growth  were  found  in  the  sun, 
as  shown  by  both  leaf-area  and  stem-diameter,  but  this  was  more  or 
less  obscured  by  the  fact  that  elongation  is  more  marked  in  the  shade, 
resulting  in  taller  stems  in  these  two  stations.  The  relation  involved  is 
best  shown  by  the  ratio  between  width  and  length  of  stem,  which  is  1  :  27 
for  the  sun,  1  :  64  for  half-shade,  and  1  :  70  for  full  shade.  While  there 
was  considerable  variation  between  the  behavior  of  the  sealed  phytometers 
and  the  unsealed  checks,  these  were  in  complete  agreement  as  to  the 
response  in  each  station. 

Dry  Weight  and  Water  Requirement. 

The  average  dry  weights  of  the  whole  plants  as  well  as  of  the  different 
organs  are  entirely  consistent  for  both  phytometers  and  checks  in  decreasing 


Transpiration  ___  _  Temperature  _ _ „ _ , _ Wind 

-  Evaporation  - - Humidity 


Fig.  30. — Average  transpiration  of  sunflowers,  shade  station,  1923,  compared  with 

factor  data;  values  as  in  fig.  28. 

from  the  sun  to  the  shade  station  (table  18).  The  sole  exception  occurs  in 
the  half-shade  stems,  in  which  maximum  length  has  already  been  noted. 
This  does  not  hold  for  the  checks,  or  for  the  whole  plant  or  shoot,  for  which 
the  response  follows  the  sequence  of  the  stations.  For  example,  the  average 
dry  weight  for  the  shoot  in  both  phytometer  and  check  was  1.64  grams  in 
the  sun,  1.06  grams  in  the  half-shade,  and  0.27  grams  in  the  full  shade. 
The  average  water  requirement  exhibited  a  similar  relation,  the  respective 
figures  being  805,  486,  and  125. 

Soil- Air. 

The  possible  effect  of  the  seal  under  the  different  habitat  complexes  was 
tested  by  removing  20  liters  of  air  through  the  long  tube  at  frequent  inter¬ 
vals,  the  first  liter  being  used  to  sweep  the  tubing  free  of  residual  air.  As 
a  further  check,  the  analyses  were  always  made  in  duplicate.  The  soil-air 
in  the  blank  containers  was  regularly  more  nearly  of  the  composition  of 
atmospheric  air  than  that  found  in  the  phytometer  containers.  There  was 


62 


SEASON  OF  1923. 


no  constant  difference  in  composition  at  the  three  stations,  the  carbon 
dioxid  averaging  about  2  per  cent  and  the  oxygen  about  20  per  cent.  The 
former  was  but  little  different  from  the  value  found  in  the  soil  with  the 
free  checks,  which  ranged  from  1  to  1.5  per  cent  at  a  decimeter  deep.  As 
a  rule,  however,  the  soil-air  from  the  phytometers  and  the  blank  checks 
departed  further  from  the  composition  of  ordinary  air  at  the  two  shade 
stations  than  in  the  sun.  This  was  probably  a  result  of  the  readier 
ventilation  of  the  containers  in  the  sun,  as  a  consequence  of  the  greater 
daily  fluctuations  in  temperature. 

SECOND  SERIES. 

Stations  and  Installation. 

The  stations  and  the  instrumental  installation  were  the  same  as  for  the 
first  series.  Seeds  from  the  same  lot  also  were  planted  on  July  5,  and  after 
a  period  of  growth  the  seedlings  were  transferred  to  small  containers  on 
July  8  and  sealed  the  following  day.  The  transpiration  per  leaf-area  during 
this  time  was  computed  for  each  of  the  118  plants  available  (table  20). 
As  with  the  first  series,  the  individuals  with  too  wide  a  departure  in  water- 
loss  were  discarded;  the  following  were  selected,  placed  in  permanent  con¬ 
tainers  on  August  2,  and  organized  into  equivalent  batteries  for  the 
respective  stations  (table  2). 


Table  2. — Transpiration  of  phytometer  plants. 


Sun  station. 

Half-shade  station. 

Shade  station. 

No. 

Amount. 

No. 

Amount. 

No. 

Amount. 

c.  c. 

c.  c. 

c.  c. 

3 . 

0.68 

1 

0.65 

2 

0.66 

6 . 

.61 

19 

.67 

9 

.64 

26 . 

.61 

20 

.60 

23 

.60 

28 . 

.60 

40 

.64 

31 

.63 

50 . 

.65 

47 

.64 

49 

.63 

70 . 

.69 

53 

.69 

54 

.63 

77 . 

.62 

79 

.66 

76 

.67 

99 . 

.64 

84 

.63 

94 

.69 

107 . 

.67 

101 

.63 

103 

.60 

113 . 

.67 

110 

.62 

108 

.69 

Average. . . 

.644 

.643 

.644 

The  average  leaf-area  of  the  plants  in  the  respective  batteries  was  25.7 
sq.  cm.  for  the  sun  station,  29.2  for  the  half-shade,  and  28.9  for  the  full- 
shade.  These  areas  include  the  cotyledons,  which  were  removed  before 
placing  the  plants  in  the  final  containers  and  hence  do  not  appear  in  the 
later  areas.  Since  the  cotyledons  have  a  slightly  different  ratio  between 
leaf-product  and  leaf-area  from  that  of  the  leaves,  and  the  rate  of  water- 
loss  differs  also,  they  were  removed  in  the  first  series  and  the  leaf-product 
alone  considered  in  the  initial  selection.  In  the  second  series  they  were  not 
removed  until  after  the  selection  was  made,  and  in  consequence  the  leaf-area 
rather  than  the  leaf-product  was  employed  in  computing  the  transpiration 
rates. 


SECOND  SERIES. 


63 


Temperature. 

The  period  of  the  second  series  was  slightly  cooler  than  that  of  the  first 
and  was  marked  by  an  exceptionally  large  proportion  of  damp,  cloudy 
weather.  The  day  averages  were  2°  to  3°  lower,  but  the  24-hour  averages 
were  only  about  a  degree  less,  the  values  for  the  shade  station  being  practi¬ 
cally  identical.  The  day  temperatures  averaged  61.6°,  59.6°,  and  58.2°  from 
sun  to  shade,  the  night  53°,  51.5°,  and  51°,  and  the  24-hour  57.2°,  55.5°, 
and  54.3°.  However,  the  differences  were  less  constant  than  in  the  first 
series  and  temperature  was  correspondingly  less  efficient  in  the  phytometer 
behavior  during  this  period  (fig.  25). 


—  Sun - Half-shade - Shade 

Fig.  31. — Average  leaf-area  of  sunflowers,  first  series,  1923. 

The  soil  temperatures  likewise  showed  the  changed  conditions  due  to 
almost  continuous  cloud  and  rain.  The  gravel  soil  of  the  sun  station 
dropped  from  57.3°  to  45.5°,  while  the  leaf-mold  of  the  shade  fell  only  2°, 
from  54°  to  52.2°.  The  average  for  the  sun  was  likewise  lower  than  in  the 
shade,  but  the  difference  was  less  than  a  degree,  while  the  average  air- 
temperature  was  more  than  3°  higher  at  the  former.  This  was  in  marked 
contrast  to  the  first  series. 

Humidity  and  Evaporation. 

The  figures  for  relative  humidity  are  even  less  significant  than  in  the  first 
series,  owing  to  the  fact  that  the  hygrograph  is  especially  erratic  during 
very  humid  weather  in  a  dry  region,  as  a  consequence  of  the  extreme 
fluctuations  within  a  few  hours.  While  the  relation  between  the  half-shade 
and  shade  stations  is  normal,  the  latter  being  constantly  5  per  cent  higher, 


64 


SEASON  OF  1923. 


there  seems  no  logical  explanation  of  a  value  5  per  cent  higher  still  in  the 
sun.  The  chief  value  of  the  results  lies  in  showing  that  the  humidities 
during  the  second  series  averaged  about  15  per  cent  higher  than  for  the 
first.  On  the  other  hand,  the  average  wind  movement  was  much  lower 
for  this  series,  being  less  than  half  as  much  for  the  sun  station,  where  it 
was  5.1  miles,  in  contrast  to  12.3  miles  per  day.  The  amount  for  the  half¬ 
shade  was  1.9  and  for  the  full-shade  but  0.03  mile. 


- Sun - Half-shade - Shade 

Fig.  32. — Average  stem-length  of  sunflowers,  first  series,  1923. 


The  effect  of  the  continuously  rainy  weather  in  reducing  and  equalizing 
evaporation  was  marked  (fig.  26).  The  latter  was  reduced  more  than  half 
in  the  sun  and  half-shade  stations,  the  respective  figures  for  the  two  series 
being  18.5  and  8.1  c.  c.,  and  9.8  and  3.9  c.  c.  The  reduction  was  naturally 
less  in  the  shade  station,  viz,  from  5.2  to  3.4  c.  c.,  the  most  significant  fact 
being  the  close  agreement  between  the  two  shade  stations.  In  spite  of  this, 
the  sequence  of  the  three  stations  was  the  same  in  both  series,  namely,  sun, 
half-shade,  and  full-shade. 

Light. 

The  light  intensities  during  the  second  series  were  measured  chiefly  by 
the  stop-watch  photometer,  hourly  readings  being  made  in  the  three  stations 
on  a  considerable  number  of  days.  The  average  intensity  for  a  12-hour 
day  on  September  2  was  0.4,  0.1,  and  0.01  in  terms  of  meridian  sunlight  on 
the  same  day,  the  relative  values  for  sun,  half-shade,  and  shade  being  100 
per  cent,  25  per  cent,  and  2.5  per  cent  respectively.  Noon-day  values  on 


RESULTS. 


65 


August  30  were  0.3,  0.15,  and  0.03,  while  the  7  a.  m.  readings  were  0.25, 
0.07,  and  0.001,  and  the  5  p.  m.  ones  0.15,  0.05,  and  0.001  respectively,  the 
greatest  divergence  coinciding  with  low  altitudes  of  the  sun.  The  values 
obtained  by  means  of  the  chemical  photometer  were  in  much  closer  agree¬ 
ment  with  these  than  was  the  case  in  the  first  series,  the  relative  percentages 
being  100  for  sun,  21  for  half-shade,  and  3  for  full-shade  (fig.  37). 

Transpiration. 

The  water-loss  was  not  only  highest  at  the  sun  station  as  for  the  first 
series,  but  it  was  also  much  higher  for  the  half-shade  than  for  the  shade. 
The  respective  averages  per  square  decimeter  of  leaf-area  were  8,  4.5,  and 
1.35  grams;  the  sun  station  ranged  from  1  to  7  grams  more  than  the  half- 


- Sun - Half-shade  - Shade 

Fig.  33. — Average  stem-width  of  sunflowers,  first  series,  1923. 

shade,  and  the  latter  from  2  to  5  grams  more  than  the  full-shade  (fig.  27). 
The  agreement  between  the  curve  of  transpiration  and  that  of  evaporation 
in  the  sun  is  slight,  but  there  is  a  general  correlation  of  the  former  with 
the  curves  for  humidity  and  temperature  (figs.  27  to  30). 

Growth. 

When  both  phytometers  and  checks  are  taken  into  account,  the  leaf-area 
was  highest  at  the  sun  station,  least  at  the  shade,  and  intermediate  in  the 
half-shade  (plate  8).  The  percentage  of  increase  was  in  the  same  order, 
the  sun  station  with  an  average  of  55  per  cent  being  twice  as  high  as  the 
shade  station  with  25  per  cent;  the  checks  in  the  half-shade  gave  35  per 
cent,  the  low  figures  for  the  phytometers  being  the  result  of  accidents 


66 


SEASON  OF  1923. 


during  the  last  two  weeks  (fig.  34).  The  order  for  stem-length  was  exactly 
the  reverse  of  that  for  the  leaf-area,  the  shade  station  being  first  with  235 
mm.,  the  half-shade  next  with  210  mm.,  and  the  sun  last  with  169  mm.  (fig. 
35).  Again,  because  of  the  inverse  relation  of  length  and  width,  the  stem 
diameter  varied  in  the  opposite  direction  (fig.  36)  ,  being  greatest  at  the  sun 
station  (3.8  mm.),  intermediate  in  the  half-shade  (3.3  mm.)  and  least  in 
the  full-shade  (2.6  mm.).  With  a  single  exception,  the  unsealed  phy- 
tometers  or  checks  gave  higher  values  than  the  sealed  ones,  indicating  that 
the  growth  of  the  latter  during  such  a  humid  period  may  have  been  retarded 
by  faulty  aeration.  However,  this  is  hardly  confirmed  by  determinations 
of  the  composition  of  the  soil-air;  the  amount  of  carbon  dioxid  was  usually 
highest  in  the  half-shade,  intermediate  in  the  sun,  and  least  in  the  full-shade. 
The  amount  varied  from  0.6  per  cent  to  nearly  4  per  cent,  the  blank  checks 
usually  yielding  about  four-fifths  as  much  as  the  phytometers. 


Fig.  34. — Average  leaf-area  of  sunflowers,  second  series,  1923. 


Dry  Weight  and  Water  Requirement. 

The  average  dry  weights  again  decreased  in  the  order  of  the  stations 
from  sun  to  shade,  the  single  exception  being  that  phytometer  roots  in  the 
half-shade  gave  a  higher  value  than  in  the  sun  (table  18).  The  respective 
values  for  the  three  stations  for  the  whole  phytometers  were  1.03,  0.98,  and 
0.41  grams,  and  for  the  check  shoots  0.82,  0.37,  and  0.26  gram.  For  the 
sun  and  half-shade  stations  the  dry  weights  were  only  about  half  those  for 
the  first  series,  while  for  the  full-shade  they  were  slightly  higher,  the  differ¬ 
ences  between  the  stations  being  consequently  much  smaller.  This  is 
reflected  in  the  water  requirement,  the  demands  for  water  in  sun  and  half¬ 
shade  being  only  about  a  fifth  as  much  as  in  the  first  series,  and  in  the 
full-shade  about  half  as  much.  The  values  in  the  order  of  the  stations  were 
165,  94,  and  59. 


SHORT-PERIOD  PHYTOMETERS. 

The  short-period  phytometer  is  one  that  is  operated  for  a  few  hours  or 
days  in  contrast  to  months  or  an  entire  season.  It  regularly  makes  use  of 
a  single  function,  such  as  transpiration,  instead  of  more  complex  ones,  such 
as  growth  or  yield.  Growth  and  short-period  phytometers  are  comple¬ 
mentary,  but  the  latter  are  so  much  simpler  to  install  and  operate  that  they 
have  a  much  wider  usefulness  for  the  solitary  investigator.  Their  advan¬ 
tages  are  many,  by  virtue  of  the  simpler  equipment  needed,  the  briefer 
period  of  exposure,  and  the  utilization  of  single  functions.  In  the  matter 
of  equipment,  the  containers  may  be  smaller  and  lighter,  and  hence  more 
easily  transported,  since  the  plants  do  not  remain  in  them  for  a  long  period 


Fig.  35. — Average  stem-length  of  sunflowers,  second  series,  1923. 

and  there  is  less  risk  of  their  becoming  root-bound  or  suffering  from 
deficient  aeration.  Sealing  is  a  much  simpler  and  more  certain  process,  and 
there  is  less  danger  of  cracking  and  consequent  absorption  of  water.  The 
smaller  containers  make  it  possible  to  use  smaller  and  more  portable  bal¬ 
ances  and  permit  greater  accuracy  in  weighing,  owing  to  the  reduced  load. 

The  short  period  is  especially  advantageous  in  reducing  the  chance  of 
accidents  of  all  sorts,  particularly  from  wind  and  hail.  It  avoids,  or  at 
least  minimizes,  undesirable  changes  in  the  soil-air  in  consequence  of  the 
seal  and  insures  much  more  normal  growth  and  behavior.  It  renders  it 
possible  to  expose  the  plants  to  uniform  conditions  or  to  a  desired  set, 
and  avoids  the  complication  of  a  sudden  change  in  factors.  A  marked 
advantage  resides  in  the  fact  that  an  abnormal  season  can  not  convert  an 
expensive  and  time-consuming  seasonal  installation  into  a  more  or  less  com¬ 
plete  disappointment,  as  happened  in  1923  at  the  Alpine  Laboratory.  The 
short-period  phytometer  enables  one  to  employ  plants  at  any  stage  of 

67 


68 


SHORT-PERIOD  PHYTOMETERS. 


development  and  to  select  uniform  individuals  with  the  minimum  effort; 
the  periods  can  be  regulated  so  that  growth  enters  little  or  not  at  all  as  a  dis¬ 
turbing  factor.  The  periods  permit  the  closest  analysis  of  behavior  with 
respect  to  any  particular  function,  intervals  of  a  few  minutes  being  as 
feasible  as  those  of  hours  or  days.  However,  it  must  be  recognized  that  the 
closer  the  scrutiny,  the  more  exacting  the  schedule  of  weighing,  or  meas¬ 
urement,  and  factor  determinations.  Finally,  an  expensive  installation  of 
recording  instruments  is  much  less  necessary,  since  simple  thermometers, 
psychrometers,  photometers,  etc.,  are  fairly  adequate. 

Applications. 

The  short-period  phytometer  can  be  employed  to  advantage  in  any 
problem  not  too  remote  from  a  base,  but  its  greatest  usefulness  is  where 
simple  functions  are  concerned  rather  than  growth  or  yield  on  a  large  scale. 
Even  in  the  latter,  however,  it  is  an  all  but  indispensable  adjunct  of  seasonal 
pbytometers,  as  it  permits  readier  and  more  exact  analysis  of  the  factor- 
function  complex.  Within  these  limitations,  it  should  be  utilized  in  all 
projects  and  experiments  where  instruments  are  used,  since  the  interpre¬ 
tation  of  instrumental  data  must  remain  misleading,  incomplete,  or 
imperfect  without  phytometers.  This  means  that  short-period  phytometers 
are  not  only  necessary,  or  at  least  desirable,  in  all  studies  in  natural  or 
cultural  habitats,  but  also  in  control  experiments  in  greenhouse  or  labora¬ 
tory,  and  as  much  or  even  more  in  investigations  in  such  applied  sciences 
as  agronomy,  horticulture,  forestry,  grazing,  etc. 

Of  all  the  functions  that  can  be  employed  as  measures,  transpiration  is 
by  far  the  most  satisfactory;  partly  because  it  can  be  readily  and  accurately 
determined  without  placing  the  plant  under  abnormal  conditions,  and 
partly  because  of  the  basic  importance  of  the  water  relation  as  well  as  its 
great  variability.  In  these  respects,  photosynthesis  as  measured  in  terms 
of  photosynthate  stands  next,  but  this  method  still  leaves  much  to  be 
desired  in  the  matter  of  accuracy,  while  the  gas  method  necessarily  modifies 
habitat  factors  seriously.  This  is  likewise  true  of  the  use  of  respiration  as 
a  measure,  and  the  latter  also  suffers  by  having  no  such  direct  relation  to 
water  or  light.  Germination  may  be  utilized  as  a  measure  of  the  chresard 
and  of  surficial  soil-temperatures.  Movements  have  also  been  employed, 
as  in  the  case  of  the  opening  and  closing  of  flowers,  carpotropic  movements, 
the  opening  and  closing  of  stomata,  etc. 

Methods. 

The  selection  of  species  for  use  as  short-period  phytometers  is  determined 
largely  by  the  object  in  view  and  the  function  to  be  utilized.  In  the  case 
of  comparative  studies,  standard  plants  such  as  sunflower  and  beans  are 
to  be  preferred,  while  in  the  accurate  interpretation  of  relations  it  is  often 
desirable  to  make  use  of  the  very  species  to  be  investigated,  such  as  wheat, 
corn,  alfalfa,  native  grasses,  forbs,1  etc.  Special  qualities  and  conditions 


1  The  term  “forb”  is  here  used  for  herbs  other  than  grasses  in  order  to  afford  a  clear  cut  dis¬ 
tinction  and  at  the  same  time  avoid  an  awkward  phrase.  It  is  derived  from  the  Greek-Latin 
root  which  appears  in  and  in  herba  (*ferb — ). 


METHODS. 


69 


must  often  be  taken  into  account  likewise;  for  example,  in  the  present  series 
made  toward  the  end  of  the  season  in  the  montane  zone,  Cyclamen  proved 
the  most  satisfactory  of  the  several  species  available,  owing  to  the  nature 
and  position  of  its  leaves.  The  individual  plants  should  be  selected  on  the 
basis  of  similarity  in  behavior  as  determined  by  actual  measurement  under 
uniform  conditions,  and  in  the  case  of  longer  series  this  should  be  checked, 
preferably  at  the  end  of  the  experiment.  Converting  the  plant  into  a  phy¬ 
tometer  is  a  much  simpler  matter  than  previously  indicated,  an  impervious 
container  of  convenient  size  and  a  wax  seal  sufficing  in  most  cases.  When 
the  period  covers  several  days  or  more,  especially  under  strong  insolation, 


Fig.  36. — Average  stem-width  of  sunflowers,  second  series,  1923. 

a  tube  is  required  for  watering  and  aerating  the  soil.  The  minimum  num¬ 
ber  of  plants  for  a  battery  should  be  3,  though  5  or  10  insure  better  results. 
The  plants  are  grouped  in  each  spot  in  such  a  way  as  not  to  affect  each 
other,  but  to  be  under  essentially  uniform  conditions,  though  when  the 
latter  vary  considerably  it  is  sometimes  better  to  scatter  the  plants.  When 
the  installation  is  a  large  one  in  distinct  habitats,  recording  instruments  are 
all  but  indispensable,  but  in  the  more  intimate  analysis  with  short-period 
phytometers,  the  thermometer,  psychrometer,  atmometer,  anemometer, 
photometer,  and  geotome  suffice  in  the  great  majority  of  cases. 

Short-period  phytometers  lend  themselves  most  readily  to  hourly 
determinations  through  the  day  or  daily  ones  for  a  week  or  so,  as  well  as 
to  the  obtaining  of  morning  and  afternoon  or  day  and  night  values. 
Obviously,  intervals  of  a  half-hour  or  less  or  2  to  3  hours  are  often  desirable. 
When  the  period  is  longer  than  a  week  or  10  days,  the  container  must  be 


70 


SHORT-PERIOD  PHYTOMETERS. 


larger  and  the  phytometer  made  with  greater  care,  so  that  it  approaches 
the  growth  type  in  many  respects.  The  detailed  application  of  the  method 
is  of  the  widest,  ranging  from  transpiration  and  other  measurements  in 
distinct  climatic  or  serai  habitats  at  the  one  end  to  the  detailed  analysis  of 
minute  habitat  areas  at  the  other.  It  has  been  employed  for  measuring  the 
efficient  factors  in  sun  and  shade,  at  different  altitudes,  on  opposite  slope- 
exposures,  in  different  forest  layers,  in  the  shade  or  in  the  crown  of  different- 
shrubs  and  trees,  above  various  covers  or  soil  surfaces,  at  different  angles 
of  slope,  etc.  In  short,  it  gives  results  of  value  wherever  factor  differences 
exist. 


- -  Sun  - Shade 

- Ha  If- shade 

Fia.  37. — Light  intensity  in  terms  of  meridian  sun, 

August  26,  1923. 

Installation  for  1923. 

The  continuously  rainy  summer  interfered  with  the  experiments  planned 
for  short-period  phytometers,  and  favorable  sunny  conditions  were  avail¬ 
able  only  in  September  and  near  the  close  of  the  season.  This  limited  the 
choice  of  species  in  the  first  place,  and  practically  all  of  these  except  Cycla¬ 
men  were  eliminated  by  snow  and  hail.  The  thick,  semi-fleshy  leaves  of 
the  latter  made  it  especially  adapted  to  late-season  studies,  and  they 
possess  the  further  advantages  of  being  nearly  entire,  horizontal,  and  on 
much  the  same  level.  The  instrumental  installation  was  maintained  in  the 
three  major  phytometer  stations,  and  this  served  also  as  a  background  for 
readings  by  means  of  simple  instruments  in  the  temporary  stations.  The 
plants  were  transferred  to  impervious  pots,  watered  and  sealed,  and  then 
given  a  day  or  two  for  adjustment  before  being  used.  Plants  of  moderate 


RESULTS. 


71 


size  were  selected,  particular  care  being  taken  to  see  that  all  the  leaves  were 
normal  and  freely  exposed.  The  pots  employed  were  4-inch  paper  ones 
previously  coated  with  paraffin  and  sealed  by  means  of  a  collar  of  plasto- 
cene  clay  about  the  plant  and  a  layer  of  paraffin  melting  at  56°  over  the 
soil  surface.  Weighing  was  done  on  a  torsion  balance  with  a  capacity  of 
4.5  kg. ;  this  was  kept  indoors  in  a  neighboring  laboratory  to  avoid  various 
minor  disturbances.  In  the  temporary  stations  readings  of  light  and  tem- 


Sept.  18 

9-11  11- 1.30  130-3  3-530 

X 

- 

\S 

N\ 

\v 

■  ■  ■  . 

_ Sun  _ _ _ _ -.Shade 

- Half-shade 

Fig.  38. — Average  transpiration  per  leaf  prod¬ 
uct  (light  lines),  and  average  evaporation 
(heavy  lines) ;  short-period  phytometers,  Sep¬ 
tember  18,  1923. 


Fig.  39. — Average  transpiration  per  leaf  prod¬ 
uct  (light  lines),  and  average  evaporation 
(heavy  lines) ;  short-period  phytometers,  Sep¬ 
tember  20,  1923. 


perature  were  made  at  frequent  intervals,  and  evaporation  was  determined 
by  means  of  white  cylindrical  atmometers  run  in  duplicate,  the  readings 
being  averaged  and  reduced  to  standard. 

Sun  and  Shade. 

Batteries  of  four  Cyclamen  phytometers  were  installed  in  each  of  the 
three  main  stations,  sun,  half-shade,  and  shade,  on  September  16.  The 
plants  were  exposed  at  11  a.  m.  after  being  weighed  and  were  removed  and 
weighed  again  at  4  p.  m.  The  average  hourly  loss  divided  by  the  leaf- 
product  gave  the  relative  values  of  37  for  the  sun,  16  for  the  half-shade,  and 
9  for  the  full-shade  station,  the  respective  percentages  being  100,  44,  and  24 


72 


SHORT-PERIOD  PHYTOMETERS. 


(table  21).  The  same  batteries  were  again  exposed  on  the  18th  and  weigh¬ 
ings  made  at  four  intervals  from  9  a.  m.  to  5h30m  p.  m.,  from  which  the 
hourly  loss  was  computed.  The  hourly  loss  was  again  more  than  twice  as 
great  in  the  sun  as  in  the  half-shade  and  about  twice  as  much  for  the  latter 
as  for  the  full-shade  (fig.  38;  table  22).  In  general,  a  similar  relation 
obtained  between  the  evaporation  at  the  three  stations;  this  was  in  har¬ 
mony  with  the  light  and  temperature  readings,  with  the  exception  that  the 
shade  station  was  slightly  warmer  than  the  half-shade. 


40 


35 


30 


25 


20 


15 


10 


5 

0 

- _ North  - — South 

Fig.  40. — Average  transpiration  per  leaf  product 
(light  lines),  and  average  evaporation  (heavy 
lines);  short-period  phytometers,  September 
26-27,  1923. 

On  September  21  all  the  phytometers  were  placed  on  level  gravel  soil 
in  full  sunshine  from  9h40m  to  llh40ra  a.  m.  to  determine  the  individual 
variability  and  to  permit  grouping  them  in  batteries  of  similar  average 
loss  (table  24).  They  were  then  exposed  in  full  sun,  half-shade  with  many 
sun-flecks  beneath  birch  ( Betula  occidentalis) ,  and  deep  shade  under  spruce 
(• Picea  engelmanni),  where  there  were  no  sun-flecks  and  practically  no 
ground  cover.  The  respective  values  were  120,  48,  and  11,  the  percentages 
being  100,  39,  and  9.  Evaporation  was  relatively  more  marked  in  the  shade 
stations,  the  respective  percentages  being  55  and  29.  This  is  readily 
explained  by  the  fact  that  the  differences  in  temperature  between  the  three 
stations  were  small,  while  the  light  intensity  decreased  greatly. 


fl.30_  Sept.  26-27  6p.m.- 

11:30  a.m.  ir.45-3  p.m.  3-6p.m.  6:45a.m. 

/  7 

/ 

1 

\ 

/ 

/ 

/ 

\  \ 

\  \ 

\  \ 

_ ^ _ 

/ 

/ 

\ 

\ 

\ 

A 

< 

/ 

/ 

/ 

/ 

/ 

\ 

X  X 

\ 

\ 

N 

Ax 

RESULTS. 


73 


Surface,  Slope,  Exposure,  and  Altitude. 

Four  batteries  of  Cyclamen  phytometers  were  installed  within  a  few 
yards  of  each  other  in  as  many  different  situations  on  September  20.  Two 
were  placed  on  the  level,  one  in  a  short  bluegrass  turf,  the  other  on  bare 
gravel;  the  other  two  were  put  on  a  bare  gravel-slope  facing  the  south. 
In  one  the  leaves  were  maintained  in  the  usual  horizontal  position,  while 
in  the  other  the  plants  were  shifted  each  hour  to  keep  the  leaves  at  right 
angles  to  the  sun’s  rays.  An  unexpected  disturbing  factor  entered  by  virtue 
of  the  fact  that  the  phytometers  on  the  bare  gravel  wilted  somewhat 
during  the  middle  of  the  day,  and  this  resulted  in  a  decrease  in  the  rate  of 
transpiration.  Hence,  while  the  phytometers  gave  conclusive  evidence  of 
the  more  xerophytic  conditions  above  the  gravel,  this  appeared  in  the 
figures  for  transpiration  only  during  the  first  and  last  period  (fig.  39;  table 
23).  On  the  contrary,  evaporation  above  the  gravel  was  slightly  lower 
than  for  the  turf  during  the  first  period,  but  it  then  rose  more  rapidly  and 
was  more  than  twice  as  great  from  3h30m  to  4h30m  p.  m.  The  phytometers 
with  the  leaves  at  right  angles  to  the  sun’s  rays  gave  a  consistently  higher 
water-loss  throughout  the  day,  the  divergence  from  the  horizontal  leaves 
naturally  becoming  greatest  in  the  last  period,  when  the  angle  of  incidence 
was  smallest.  Evaporation  was  highest  on  the  gravel  slope,  owing  to  its 
south  exposure,  but  it  also  fell  off  markedly  during  the  last  period. 

Short-period  phytometers  of  Cyclamen  were  run  on  north  and  south  slope- 
exposures  of  Engelmann  Canyon  at  the  Alpine  Laboratory  from  8h30m 
a.  m.  September  26  to  6h45m  a.  m.  September  27,  the  distance  between  the 
two  stations  being  about  100  yards.  As  was  to  be  expected,  the  south 
exposure  was  found  to  be  both  drier  and  warmer  than  the  north  throughout 
the  day  and  night,  though  the  temperature  difference  at  night  was  naturally 
much  smaller.  The  general  agreement  between  temperature,  light,  and 
evaporation  on  the  one  hand  and  transpiration  on  the  other  was  good,  the 
curves  of  the  latter  being  flattened  by  the  fact  that  maximum  light  intensity 
came  much  earlier  in  the  day  than  the  maxima  for  temperature  and 
evaporation  (fig.  40;  table  25). 

On  September  22,  batteries  of  Cyclamen  phytometers  were  exposed 
simultaneously  in  full  sunshine  at  the  Alpine  Laboratory,  8,100  feet,  and 
at  Windy  Point  on  Pike’s  Peak  at  an  altitude  of  12,500  feet.  In  spite  of 
considerable  differences  in  temperature,  the  transpiration  and  evaporation 
were  nearly  the  same,  being  only  slightly  greater  at  the  lower  elevation. 
This  is  in  contrast  to  earlier  studies  (Clements,  1908),  which  gave  higher 
values  on  alpine  summits,  evidently  in  response  to  reduced  air-pressure, 
and  is  probably  to  be  explained  by  the  prevalence  of  snow  at  this  late  date. 


RELATED  APPLICATIONS  OF  THE  PHYTOMETER 

METHOD. 

SLOPE-EXPOSURE  STUDIES. 

The  marked  differences  of  vegetation  on  opposite  slopes  have  often  been 
noted,  but  no  comprehensive  and  thoroughgoing  analysis  of  the  physical 
factors,  growth  relations,  and  community  behavior  had  been  made  before 
the  present  study  (Clements  and  Lutjeharms,  1921-1923;  Lutjeharms, 
1924).  In  mountain  regions  of  the  West  in  particular,  the  difference 
between  northerly  and  easterly  slopes  on  the  one  hand  and  southerly  and 
westerly  ones  on  the  other  may  amount  to  a  whole  climax,  the  dry-warm 
slope  being  subclimax  to  the  general  climax  or  the  moist-cool  slope  exhibiting 


Maximum -  Maximum - 

Minimum - Minimum - - - - 

Fig.  41. — Comparison  of  air  and  soil  temperatures  on  north 
(light  lines)  and  south  (heavy  lines)  slope-exposures, 
Alpine  Laboratory. 


a  postclimax  (Plant  Succession,  109;  Plant  Indicators,  88).  Such  relations 
are  fundamental  to  the  investigation  of  changes  of  climate  and  vegetation, 
and  hence  to  the  phylogeny  of  climaxes.  They  have  come  to  play  an 
increasingly  important  part  in  the  comparative  evolution  of  formations  and 

74 


SLOPE-EXPOSURE  STUDIES. 


75 


associations,  and  this  has  rendered  it  advisable  to  employ  definite  terms 
for  the  two  types  of  slope-exposure,  especially  since  the  terms  drawn  from 
direction  are  often  awkward  and  their  significance  is  reversed  for  the 
northern  and  southern  hemispheres.  Regardless  of  exposition,  the  dry-warm 
slope  is  designated  the  xerocline  (£77/06?,  dry;  *AiW  slope)  and  the  moist- 
cool  slope  the  mesocline  (/ueo-o?,  mid,  hence  moist) . 

Installation. 

An  unusually  favorable  opportunity  for  slope-exposure  studies  was 
afforded  by  Engelmann  Canyon,  in  which  the  Alpine  Laboratory  is  situated. 
This  is  a  long,  narrow  canyon  on  the  east  slope  of  Pike’s  Peak,  extending 
from  the  foothills  at  7,000  feet  to  an  altitude  of  9,000  feet.  In  consequence, 


14 

13 

12 

ii 

10 

9 

8 

7 

6 

5 

4 

3 

2 

I 

0 


it  has  constituted  a  highway  for  the  movement  of  grassland  and  plains 
species  upward  along  the  xerocline  during  dry  phases  of  the  climatic  cycle 
and  of  montane  and  subalpine  ones  downward  during  wet  phases.  In  the 
vicinity  of  the  Laboratory  to-day,  the  north  exposure  is  covered  with  a 
practically  pure  forest  of  Douglas  fir  ( Pseudotsuga  mucronata) ,  while  the 
south  exposure  is  a  mictium  of  grassland  and  chaparral,  dotted  with  yellow 
pines  ( Pinus  ponderosa ) ,  scattered  Douglas  fir,  and  occasional  limber  pines 
( Pinus  fiexilis).  Extensive  thickets  of  chaparral,  consisting  chiefly  of 
Quercus,  Holodiscus,  and  Primus ,  occur  in  the  more  stable  areas,  but  for  the 
most  part  the  slope  is  occupied  by  an  open  bunch-grass  community  of 
Elymus  triticoides,  Muhlenbergia  gracilis,  and  Andropogon  scoparius ,  with 


Mesocline _ _ Canyon  bottom _ _ Xerocline 


13 

37 

'O': 

3(18) 

io: 

■ 

59.9(22)'t 

24  9. 
T  (2 

695  08) 

706  686  (Z7) 

72 

Z 

,6.6 

(22) 

5.9  (26) 

5.5  (22) 

4. 

6(18) 

37 

■ 

.0 

3G>3. 

_ 

188 

183(4) 

125  (4) 

137 

■  • 

J 

|  86  (4) 

June  July  August  June  July  August  June  July  August 
_—^i  Total  miles-wind  velocity 

. .  Evaporation-cc. 

mum a  Grams  oxalic  acid  oxidized  by  light 

C  )  Numberof  days  when  less  than  a  month 

Fig.  42. — Monthly  value  for  wind,  evaporation,  and  light  in  slope-exposure  transect. 


76 


RELATED  APPLICATIONS. 


relict  areas  of  Agropyrum  glaucum,  Bouteloua  gracilis,  and  Elymus  cana¬ 
densis,  and  numerous  subdominants  from  the  plains. 


Fig.  43. — Comparison  of  holard  percentages  in  slope-exposure  transect;  south 
slope-exposure  (heavy  lines),  north  (medium  lines),  bottom  of  canyon  (light 
lines). 


Two  stations  were  located  directly  opposite  each  other,  at  a  height  of 
about  500  feet  above  the  bottom  of  the  canyon,  where  the  third  station  was 
installed  near  the  brook.  Complete  batteries  of  instruments  were  placed  in 
each  of  the  stations  and  continuous  records  obtained  of  the  following 


SLOPE-EXPOSURE  STUDIES. 


77 


factors:  (1)  air-temperature,  (2)  soil-temperature  at  depths  of  4  and  12 
inches,  (3)  relative  humidity,  (4)  evaporation,  (5)  wind,  (6)  light  intensity, 
(7)  precipitation,  and  (8)  holard.  Several  native  and  cultivated  species, 
including  some  shrubs,  were  employed  as  phytometers,  but  the  best  results 
were  obtained  with  the  sunflower.  The  functions  utilized  were  transpira¬ 
tion,  photosynthesis,  and  growth,  in  terms  of  stem-height,  diameter,  leaf 
length  and  width,  dry  weight,  and  water  requirement.  The  detailed  results 
of  the  investigation  are  now  being  published  (Lutjeharms,  1924),  and  a 
brief  summary  will  suffice  here. 

Summary. 

The  efficient  factors  gave  the  following  differences  for  the  xerocline  in 
comparison  with  the  mesocline  (figs.  41  to  43). 


Air-temperature  (average  of  maximum  and  minimum  readings) . +  2° 

Soil-temperature  (average  of  maximum  and  minimum  readings) . +11° 

Average  daily  soil-temperature  at  12  inches . . +16° 

p.  ct. 

Light,  evaporation,  and  wind,  each  approximate . +  50 

Average  humidity . —  6 

Holard  at  0  to  6  inches . —  36 

Holard  at  6  to  18  inches . —  26 


The  transpiration  and  growth  of  phytometers  during  the  entire  season 
gave  the  following  values  for  the  xerocline  (plate  9;  figs.  44,  45) : 

p.  ct. 


Average  leaf -area  per  phytometer . +  14 

Average  stem-diameter  per  phytometer . -J-  10 

Average  stem-height  per  phytometer . —  25 

Average  dry-weight  per  phytometer . +  75 

Average  transpiration  per  phytometer . +  82 


For  phytometers  grown  half  as  long  and  during  the  latter  part  of  the 
summer,  the  values  were  as  follows: 

p.ct. 


Average  leaf-area  per  phytometer . +  71 

Average  stem-diameter  per  phytometer . +  10 

Average  stem-height  per  phytometer . —  13 

Average  dry-weight  per  phytometer . +  38 

Average  transpiration  per  phytometer . . . +130 

Average  carbohydrate  reserves  in  milligrams  of  dextrose . +  32 


The  preceding  instrumental  and  phytometer  results  make  it  clear  why 
the  south  slope-exposure  is  covered  with  the  scrub  and  grassland  dominants 
of  foothill  and  plains,  while  the  north  one  is  dominated  by  the  charac¬ 
teristic  montane  forest  of  this  climatic  zone.  They  also  serve  to  explain 
the  reason  for  the  dry-phase  invasion  along  the  xerocline  and  the  wet-phase 
movement  down  the  mesocline,  as  well  as  in  the  bottom  of  the  canyon. 


Transpiration  and  Growth  in  the  Grassland  Climax. 

PHYTOMETER  BATTERIES. 

In  order  to  obtain  further  light  as  to  the  climatic  differences  of  the  major 
stations  in  terms  of  functional  response,  a  special  investigation  was  made  of 
transpiration  and  growth  (Clements  and  Weaver,  1924).  Plants  of  Helian - 
thus  annuus,  Avena  sativa,  Elymus  canadensis,  and  Acer  negundo  were  grown 
from  seed  or  transplanted  as  seedlings  into  sheet-metal  containers  of  appro- 


Dry  weight - Transpiration 


Fig.  44. — Average  dry  weight  and  transpiration  of  phytometers 
in  slope-exposure  transect;  south  slope-exposure  (heavy 
lines),  north  (medium  lines),  bottom  of  canyon  (light  lines). 

priate  shape  and  sufficient  size  to  accommodate  the  root  systems  through¬ 
out  the  duration  of  the  experiment.  After  the  plants  were  well  established, 
the  leaf-area  and  the  weight  of  plant  and  container  were  determined.  They 
were  then  installed  at  the  several  stations,  together  with  a  complete  battery 
of  instruments,  for  a  period  of  14  days,  and  measurements  made  of  tran¬ 
spiration  and  growth  in  terms  of  increased  area.  The  considerable  differ¬ 
ences  in  altitude,  and  hence  in  seasonal  development,  made  simultaneous 
studies  undesirable,  and  consequently  the  periods  of  observation  were  suc¬ 
cessive.  This  was  also  imperative  because  of  the  time  and  effort  involved. 

78 


TRANSPIRATION  AND  GROWTH  IN  THE  GRASSLAND  CLIMAX.  79 


The  individual  plants  of  sunflower  and  box-elder  were  placed  in  cylin¬ 
drical  galvanized-iron  containers  5  to  6  inches  in  diameter  and  9  to  10 
inches  deep,  filled  with  rich  loam  soil  tamped  firmly  in  place.  A  layer  of 
0.5  inch  of  coarse  gravel  in  the  bottom  of  the  container  covered  an  exit  tube, 
consisting  of  an  automobile  tire  valve-stem  with  the  inner  end  cut  off  and 
covered  with  a  fine  copper  gauze  soldered  in  place.  The  core  of  each  tube 
had  been  removed.  The  tube  was  soldered  in  place  with  the  threads  pro¬ 
jecting  through  the  wall  of  the  container,  so  that  an  exhaust-pump  could  be 
attached  for  aerating  the  soil.  The  tube  also  assisted  materially  in  water¬ 
ing  the  plants,  the  usual  cap  preventing  loss  during  the  intervals.  The  soil 
was  well  screened,  brought  to  an  optimum  holard,  and  weighed  at  the  time 
of  filling  the  containers.  By  restoring  the  containers  to  their  original  weight 
from  time  to  time,  the  holard  was  maintained  at  the  desired  level.  To 


Mesocline _  Canyon  bottom _ _ Xerocline 


7.9 

8.7 

7. 

7 

7 

13 

6  'i 

fee 

>5 

6' 

L8 

51 

A 

496 

5.5 

4' 

» 

4< 

30 

3.3 

3< 

36 

! 

£.4 

1/ 

11 

0f3 

1!  0.47 

1  T  . 

Leaf  area  (Sq.cm.)  tixuuLiiui-n-ji  Transpiration  per.  gm.dry  weight 

Stem  height  ( mm.)  >—  . . *  Dry  weight  of  tops 

Stem  diameter  (mm.)  Dry  weight  of  roots 


Fig.  45. — Comparative  growth  and  dry  weight  of  phytometers  in  slope-exposure  transect. 


prevent  loss  other  than  by  transpiration,  the  containers  were  furnished  with 
a  sloping  metal  top  provided  with  a  circular  opening,  with  the  edges  reamed 
upward,  and  large  enough  to  receive  a  cork  2.5  inches  in  diameter.  An 
effective  seal  was  formed  by  boring  a  hole  large  enough  for  the  plant  stem, 
splitting  the  cork  and  fitting  it  into  place  after  padding  the  sides  of  the 
opening  with  a  little  cotton.  The  seal  was  tested  by  a  check  container  with¬ 
out  a  plant  but  fitted  with  a  wooden  peg  to  simulate  the  plant  stem.  During 
the  period  of  14  days  this  did  not  lose  water  in  an  amount  sufficient  to  be 
detected  by  a  balance  sensitive  to  2  grams  under  a  load  of  7  kg. 

The  containers  for  wild  rye  and  oats  were  similar  to  those  already  de¬ 
scribed,  except  for  the  tops,  which  were  furnished  with  a  slit  5  inches  long 


80 


RELATED  APPLICATIONS. 


and  1  inch  wide.  The  edges  of  the  metal  cut  in  making  the  slits  were  turned 
down  into  the  container  about  a  quarter  of  an  inch  on  each  side  and  a 
half-inch  at  the  ends  of  the  slit.  These  furnished  supports  for  narrow 
strips  of  shellacked  oak,  which  were  held  in  place  by  thin  wedges  of  similar 
material  at  each  end.  These  were  put  in  place  after  the  containers  had 
been  filled  and  the  soil  pressed  firmly  under  the  metal  tops.  They  were 
then  coated  with  shellac  so  that  no  openings  remained  except  between  the 
wooden  strips,  which  narrowed  the  slit  to  about  10  mm.  The  seeds  were 
planted  through  this  opening,  which  was  nearly  filled  with  soil  kept  moist 
by  frequent  watering.  After  the  plants  came  up,  the  remainder  of  the 
opening  was  filled  with  sand  level  with  the  top  of  the  wooden  strips.  The 
containers  were  provided  with  felt  tops,  cut  to  fit  around  the  slits,  and  sunk 
level  with  the  soil.  The  efficiency  of  the  sand-mulch  in  preventing  water- 
loss  was  found  to  be  high,  only  6  grams  escaping  in  a  period  of  2  weeks. 
Twelve  plants  of  average  size  were  selected  from  the  several  containers  and 


Table  3. — Transpiration  and  growth  at  the  three  stations. 


Species. 

Water-loss  per  sq.  dm. 

Increase  in  area. 

Rate  of  growth,  based 
on  actual  increase  in  area 

Lin¬ 

coln. 

Phil¬ 

lips¬ 

burg. 

Bur¬ 

ling¬ 

ton. 

Lin¬ 

coln. 

Phil¬ 

lips¬ 

burg. 

Bur¬ 

ling¬ 

ton. 

Lin¬ 

coln. 

Phil¬ 

lips¬ 

burg. 

Bur¬ 

ling¬ 

ton. 

gm. 

gm. 

gm. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

p.  ct. 

Sunflower . 

145 

225 

214 

409 

1,477 

4,097 

854 

860 

998 

Wild  rye . 

72 

199 

218 

239 

257 

163 

410 

549 

140 

Oats . 

99 

178 

212 

279 

246 

694 

1,155 

796 

510 

Box-elder . 

85 

159 

137 

85 

162 

220 

52 

161 

370 

Average . 

100 

190 

195 

253 

535 

1,294 

618 

591 

504 

the  leaf-area  determined.  From  this,  and  the  number  of  plants  in  each 
container,  the  initial  area  of  the  group  of  plants  in  any  container  was 
calculated.  The  final  area  was  determined  in  a  similar  manner.  This 
method  was  used  because  it  was  quite  impossible  to  determine  the  total 
area  of  the  plants  in  place,  as  could  be  done  with  the  dicotyls. 

Owing  to  cool,  wet  weather  the  plants  grew  slowly,  except  during  the 
last  week  of  May.  They  were  kept  covered  during  rains  and  at  night, 
watered  from  a  burette,  and  aerated  from  time  to  time.  To  keep  the  metal 
containers  from  heating  the  soil,  they  were  surrounded  by  sand  and  the  top 
covered  by  a  collar  of  felt  about  a  centimeter  thick,  held  in  place  by  strips 
of  adhesive  tape.  On  June  1  the  leaf-area  was  determined  by  means  of 
solio  prints  and  the  planimeter,  corks  were  inserted,  and  the  containers 
(with  collars  removed)  brought  back  to  their  initial  weight  after  they  had 
been  transported  to  the  stations  in  the  high  prairie  at  Lincoln,  and  at 
Phillipsburg  and  Burlington.  Here  they  were  placed  in  the  soil  and 
thoroughly  covered  after  the  collars  had  been  replaced,  the  exposed  plants 
being  sheltered  during  rains. 


SOD-CORE  PHYTOMETERS. 


81 


After  the  14-day  period  of  the  experiment,  following  final  weighings,  the 
number  of  parent  plants  and  number  of  tillers  in  each  container  was  ascer¬ 
tained.  Eighteen  specimens  of  each  group  were  then  selected  and  their 
areas  determined.  From  these  data  the  final  areas  were  calculated. 

This  series  proved  a  disappointment  in  so  far  as  normal  climatic  rela¬ 
tions  were  concerned,  owing  to  the  wholly  exceptional  weather.  The  amount 
of  sunshine  at  Lincoln  was  little  more  than  half  that  at  the  other  stations, 
while  the  air-temperature  averaged  10°  lower  and  the  soil-temperature 
ranged  from  11  to  15°  lower.  The  average  humidity  was  15  to  18  per  cent 
higher  and  the  evaporation  but  a  third  or  a  fourth  of  that  at  Phillipsburg 
or  Burlington.  Hence,  it  is  easy  to  understand  why  the  increase  in  area 
was  twice  as  great  at  Phillipsburg  and  more  than  four  times  as  great  at 
Burlington,  though  the  normal  relation  is  suggested  by  the  rate  of  growth 


Table  4. — Environmental  conditions  at  the  three  stations. 


Station. 

Approxi¬ 
mate  hours 
sunshine. 

Average 
day  tem¬ 
perature. 

Soil 

temper¬ 

ature. 

Average 

day 

humidity. 

Average 

daily 

evaporation. 

Wind, 
miles  per 
hour. 

0  F. 

o  p 

p.  ct. 

c.  c. 

Lincoln . 

39 

70.1 

62  to  71 

75 

8.4 

3.6 

Phillipsburg. .  . 

75 

80.6 

74  to  82 

60 

25.5 

3.3 

Burlington. . . . 

71 

80.0 

73  to  86 

57 

35.4 

3.4 

based  on  the  actual  increase  in  area  and  by  the  order  of  water-loss  at  the 
three  stations.  Thus,  while  the  plant  responses  are  in  agreement  with  the 
physical  factors  for  the  respective  fortnights  concerned,  it  is  obvious  that 
entirely  comparable  results  could  be  insured  only  by  dealing  with  the 
growth  season  for  each  species.  An  adequate  record  of  transpiration  and 
growth  for  such  a  period  at  station^  widely  separated  demands  at  least  one 
resident  investigator  for  each  station,  and  such  studies  must  await  the  future. 

COMMUNITY  PHYTOMETERS. 

Sod-Core  Phytometers. 

One  of  the  major  tasks  of  quantitative  ecology  is  to  determine  the  func¬ 
tional  responses  of  plants  when  grouped  in  communities.  While  much  light 
can  be  obtained  by  the  use  of  individual  plants  under  control  in  the  field, 
in  the  form  of  standard  phytometers,  these  differ  essentially  in  their  soil 
and  competition  relations  from  plants  growing  together  in  the  actual  cover. 
Hence,  the  task  is  to  maintain  these  natural  relations  of  the  community  and 
at  the  same  time  to  secure  a  degree  of  control  that  modifies  the  efficient 
factors  little  or  not  at  all.  In  the  case  of  transpiration,  for  example,  these 
requisites  can  be  met  only  by  weighing,  as  all  other  methods  modify  the 
physical  factors  to  an  undesirable  degree.  The  method  that  maintains  the 
soil  and  community  relations  with  the  minimum  disturbance  is  the  soil- 
block,  which  was  first  employed  for  determining  the  chresard  in  the  field 
(Clements,  1904,  1905).  This  requires  only  such  slight  modifications  as 
those  of  size  and  form  to  become  applicable  to  all  problems  in  which  an 
undisturbed  soil-root  core  is  indispensable  (Weaver  and  Crist,  1924). 


82 


RELATED  APPLICATIONS. 


In  consequence,  the  first  objective  was  to  perfect  the  soil-block  method 
so  that  it  could  be  used  in  the  field  with  both  convenience  and  accuracy. 
Because  of  its  importance  in  the  grassland  climate,  the  chief  function  to  be 
measured  was  transpiration,  though  chresard  and  aeration  can  be  studied 
with  something  of  the  same  readiness.  In  the  present  case  the  transpira¬ 
tion  from  representative  cores  was  followed  in  the  proper  climate  of  each 
association,  but  it  is  evident  that  the  containers  can  be  moved  or  exchanged 
between  different  edaphic  or  climatic  stations  and  thus  serve  as  reciprocal 
phytometers.  This  permits  the  determination  of  the  transpiration  behavior 
of  each  climax  in  its  own  climate  in  terms  of  adjustment  and  adaptation 
and  at  the  same  time  affords  a  basis  for  comparing  adjacent  climaxes.  A 
further  use  of  fundamental  value  arises  out  of  the  rainfall  relation.  The 
method  of  the  soil-core  not  only  makes  it  possible  to  trace  the  complete 
water  cycle  of  rainfall,  holard,  evaporation,  and  transpiration,  but  also  to 
estimate  the  extent  to  which  the  vegetation  of  each  region  may  furnish  the 
water- vapor  for  its  own  rainfall  (Clements,  1923).  Finally,  it  also  opens 
up  a  new  field  in  the  functional  relation  of  roots  to  the  soil  as  an  actual 
structure,  which  shows  striking  differences  from  climate  to  climate,  as  well 
as  from  one  local  habitat  to  another. 

Methods. 

A  steel  cylinder  12  inches  tall  and  with  an  inner  area  of  1  square  foot,  the 
lower  edge  of  which  was  sharpened,  was  driven  into  the  grassland  soil  to 
a  depth  of  4  inches.  Care  was  taken  to  cut  off  none  of  the  leaves  belonging 
to  the  plants  in  the  square  foot  selected,  which  was  chosen  with  a  special 
regard  to  its  representative  structure.  The  cylinder  was  then  carefully 
removed,  leaving  the  column  of  soil  intact,  and  replaced  by  one  of  heavy 
galvanized  iron  3  feet  long  and  reinforced  at  both  ends  by  a  heavy  wire 
over  which  the  metal  was  turned  back  smoothly.  After  starting  a  row  of 
these  cylinders  at  distances  of  8  inches,  a  trench  2  feet  wide  was  dug 
around  them  to  a  depth  of  over  3  feet.  In  this  process  no  soil  was  removed 
within  3  or  4  inches  of  the  cylinder.  As  the  trench  was  deepened,  the 
columns  of  soil  were  carefully  pared  away  with  large  knives  in  such  a 
manner  that  the  cylinders  could  be  forced  down  under  considerable  pres¬ 
sure  from  above.  By  shaping  the  column  for  a  few  inches  in  front  of  the 
descending  cylinder,  it  was  possible  to  force  the  latter  into  place  over  a 
tightly  fitting  soil-core  to  a  depth  of  3  feet.  The  columns  were  then 
undercut  and  smoothed  off  level  with  the  lower  end  of  the  cylinder.  A 
loose-fitting  metal  bottom  with  the  edges  2  inches  deep  was  placed  over 
the  end  and  the  entire  container  was  then  weighed  on  a  portable  Fairbanks 
scale  sensitive  to  one-fourth  pound. 

In  the  meantime  a  trench  sufficiently  wide  and  deep  to  receive  the 
cylinders  in  an  upright  position  had  been  dug  in  a  nearby  area,  care  being 
taken  not  to  cover  the  grass  with  soil.  The  containers  were  lowered  in  the 
new  trench  and  slid  into  place  on  a  plank  in  the  bottom,  after  which  the 
bottoms  were  made  water-tight  by  means  of  a  measured  amount  of  hot 
wax  of  the  usual  composition.  The  trench  was  then  filled  with  soil  and 
nieces  of  sod  were  fitted  around  the  tops  so  that  the  surface  conditions 
would  be  essentially  normal.  The  trenches  were  selected  so  that  the 


SOD-CORE  PHYTOMETERS. 


83 


surface-water  would  readily  drain  away  from  them,  and  in  addition  the 
plants  were  covered  by  wooden  roofs  whenever  rain  was  actually  falling. 
This  was  imperative  because  of  the  varying  interception  of  rainfall  by  the 
different  vegetation  in  the  several  containers.  In  the  case  of  the  cultivated 
crops,  oats  and  millet,  the  usual  type  of  bottom  was  replaced  by  one  3  feet 
deep,  owing  to  the  difficulty  of  selecting  a  proper  slope  for  drainage.  In 
order  to  determine  the  amount  of  water  evaporated  from  the  cultivated 
soil,  the  plants  were  removed  from  one  container  in  each  field.  In  another 
the  natural  grasses  were  left  in  place  after  having  been  killed  by  the  addi¬ 
tion  of  a  measured  amount  of  boiling  water  (plate  10a). 


Table  5. — Comparison  of  factors  and  average  water-loss. 


Station. 

Dominant 

grasses. 

Date  of 
experiment. 

Approxi¬ 

mate 

sunshine. 

Aver. 

day 

temp. 

Aver. 

day 

humidity. 

Aver. 

daily 

evapo¬ 

ration. 

Aver,  daily 
loss  from 
sq.  foot 
of  cover. 

Burling- 

( Bulbilis . 

p.  ct. 

o  F 

p.  ct. 

c.  c. 

lbs. 

ton. . .  . 

s  Bouteloua .  . . 

1  Agropyrum .  . 

•July  5  to  20. 

71 

80 

57 

35.4 

0.96 

Phillips¬ 
burg.  .  . 

(Bouteloua.  .  . 
(Andropogon.. 
Andropogon.. 

June  18  to 
July  3. 

75 

80.6 

60 

25.5 

1.33 

Lincoln . . 

Stipa . 

'  Koeleria . 

Bouteloua .  . . 

July  24  to 
Aug.  8. 

47 

79 

80 

22.0 

0.85 

From  time  to  time,  depending  upon  the  weather  and  the  needs  of  the 
plants,  water  in  measured  amounts  was  slowly  added  to  all  the  containers, 
and  as  a  result  there  was  little  shrinkage  of  the  core  from  the  sides  of  the 
container.  None  of  the  plants  died,  and  even  those  near  the  edges  gave  no 
signs  of  wilting,  demonstrating  that  the  roots  in  the  core  supplied  abundant 
water  for  transpiration.  Much  care  was  exercised  in  watering,  so  that  there 
was  little  or  no  runoff  down  the  sides  of  the  core.  This  was  accomplished 
by  pouring  the  water  on  slowly  and  pressing  the  moist  soil  firmly  against 
the  cylinder  wherever  the  contact  was  not  complete.  At  the  end  of  the 
period  the  containers  were  again  weighed  and  the  losses  calculated.  At  the 
end  of  the  experiment  the  vegetation  was  carefully  removed  at  the  soil 
surface  by  means  of  a  hand  grass-clipper.  The  dense  foliage  of  former 
years  was  carefully  separated  from  the  living  plants,  the  latter  oven-dried 
at  60°  C.,  and  weighed. 

Results. 

As  in  the  case  of  water-loss  from  the  phytometers,  the  exceptional  weather 
of  the  summer  obscured  the  normal  climatic  response  of  the  sod-cores. 
When  the  physical  factors  and  the  type  of  vegetation  are  taken  into  account, 
it  is  clear  why  the  low  short-grass  cover  at  Burlington  in  the  driest  climate 
transpired  less  than  the  mixed  prairie  at  Phillipsburg  in  a  moister  atmos¬ 
phere  and  more  than  the  luxuriant  true  prairie  at  Lincoln  in  a  much  more 
humid  climate.  Thus  again,  while  the  use  of  sod-cores  contributed  no 
clear-cut  evidence  as  to  the  relation  of  the  three  climaxes  and  their  climates, 
it  does  demonstrate  the  value  of  the  method  and  what  can  be  expected  of 


84 


RELATED  APPLICATIONS. 


it  when  employed  through  a  series  of  years.  The  losses  from  the  three 
crops,  while  of  interest,  have  no  comparative  value,  since  a  different  species 
was  used  in  each  station;  they  are  distinctly  helpful,  however,  in  showing 
the  similarity  in  the  behavior  of  the  native  cover  and  representative  crops 
for  each  station  and  in  potential  importance  for  the  rainfall  of  each  region. 
However,  in  the  future  development  of  the  method,  it  is  obvious  that  the 
same  dominant  and  the  same  crop  should  be  employed  throughout  the  series 
of  stations,  and  this  should  involve  the  reciprocal  transfer  of  sod-cores  and 
crop-cores  between  the  three  stations. 

FIELD-PLOT  PHYTOMETERS. 

The  field-plot  and  cut-quadrat  phytometers  have  much  in  common  when 
the  latter  is  used  for  cultivated  plants,  the  chief  difference  being  the  greater 
size  of  the  former.  The  field-plot  type  was  utilized  in  1922  and  1923  for 
measuring  the  conditions  in  dry-land  farming  and  in  irrigated  fields  in 
terms  of  root  behavior  and  yield.  The  installation  was  made  at  Greeley, 
Colorado,  in  plots  of  one-thirtieth  acre  in  fully  irrigated,  partly  irrigated, 
and  dry  land.  The  crops  employed  were  alfalfa,  spring  wheat,  sugar  beet, 
potato,  and  yellow  dent  corn.  Complete  records  were  kept  of  the  usual 
factors,  except  wind,  and  the  holard  was  determined  weekly  to  a  depth  of 
4  feet  and  at  longer  intervals  to  the  depth  of  root  penetration,  5  to  9  feet. 
As  the  dry-land  and  irrigated  areas  were  only  about  a  mile  apart,  the 
general  climatic  conditions  were  identical  and  the  soil  was  similar,  the 
efficient  differences  arising  out  of  the  irrigation.  The  development  of  the 
root  system  was  traced  at  several  intervals  during  the  growing  season, 
growth  of  shoots  measured  from  time  to  time,  and  the  yield  determined  at 
the  end  (Jean  and  Weaver,  1923,  1924). 

In  every  case  the  root  development  and  habit  were  found  to  respond 
closely  to  variations  in  the  holard,  and  the  crops  with  the  most  extensive 
root  systems  to  give  the  largest  yields.  The  general  root  behavior  may  be 
illustrated  by  wheat,  the  roots  of  which  spread  more  widely  in  the  surface 
soil  owing  to  showers,  but  died  below  2  feet  in  dry  soil,  the  corresponding 
penetration  being  3  feet  in  lightly  irrigated  and  4.3  feet  in  fully  irrigated 
soil.  The  plots  were  at  first  equally  moist  in  1923,  and  the  root  systems 
were  alike;  because  of  greater  rainfall  the  penetration  in  dry  land  was  a 
foot  greater  than  in  1922,  while  growth  in  the  irrigated  plots  was  much  the 
same  as  before.  The  respective  heights  in  dry  land,  partially  and  fully 
irrigated  plots  were  15,  41,  and  43  inches  and  the  yields  3,  32,  and  29  bushels. 
The  roots  of  corn  made  the  best  development  in  the  lightly  irrigated  plot, 
and  this  was  correlated  with  the  best  yield  of  125  bushels  per  acre,  the  yield 
being  25  bushels  for  dry  land  and  115  for  full  irrigation. 

CUT-QUADRAT  PHYTOMETERS. 

The  growth  of  a  representative  area  of  a  community  may  be  used  as  a 
climatic  index  as  well  as  a  measure  of  response  in  much  the  same  way  as 
transpiration.  It  possesses  three  distinct  advantages  over  the  latter,  though 
the  two  are  complementary  and  hence  one  can  not  replace  the  other.  Growth 
demands  no  laborious  installation,  as  it  can  be  determined  directly  from 
the  native  or  culture  community  in  position.  While  it  can  be  measured  at 


CLIP-QUADRAT  PHYTOMETERS. 


85 


any  time,  it  yields  the  major  values  at  the  end  of  the  growing-season,  and 
thus  does  not  require  the  services  of  a  resident  investigator.  Moreover,  it 
integrates  the  response  for  the  whole  season,  though  as  a  complex  it  permits 
less  ready  analysis  than  transpiration  and  is  also  less  satisfactory  for  short 
periods.  In  short,  it  is  the  simplest  and  most  convenient  of  all  community 
phytometers  when  employed  in  the  form  of  the  cut  or  clip  quadrat.  This 
is  the  only  practicable  method,  as  the  measurement  of  the  individuals  in  a 
community  group  is  too  time-consuming  to  be  desirable.  There  are  certain 
cases  in  which  it  is  profitable  to  pull  the  individuals  out  with  their  roots, 
but  this  is  hardly  feasible  in  a  close  cover  or  a  compact  soil.  The  clip- 
quadrat  is  merely  the  usual  one  of  a  square  meter  in  extent,  from  which  the 
shoots  are  cut  at  any  desired  time.  It  may  be  either  smaller  or  larger  in 
order  to  meet  special  conditions,  as  in  the  case  of  crops  planted  in  rows. 
The  growth  is  regularly  expressed  in  terms  of  dry  matter,  but  in  the  case 
of  grazing  ranges  or  forage  crops,  the  green  weight  should  likewise  be  found. 
Finally,  the  clip-quadrat  facilitates  the  analysis  of  community  response  to 
climatic  factors  by  making  it  possible  to  measure  growth  during  different 
portions  of  the  season  or  its  variations  from  season  to  season  or  from  the 
wet  to  the  dry  phase  of  a  climatic  cycle,  and  to  determine  the  part  played 
by  the  various  species  in  the  total  production. 

In  the  case  of  the  grains,  it  is  often  preferable  to  select  the  individuals  to 
be  cut  in  accordance  writh  the  results  desired,  instead  of  taking  all  those  in 
a  particular  area  (Weaver,  Jean,  and  Crist,  1922).  This  may  be  regarded 
as  an  aggregate  clip-quadrat;  it  has  the  further  advantage  of  permitting 
measurement  of  particular  individuals  throughout  the  season. 

Clip-quadrats  were  first  installed  at  the  three  stations  in  1920 ;  these  rep¬ 
resented  high  and  low  prairie  in  the  true-prairie  association,  mixed  prairie, 
and  short-grass  plains  (Weaver,  1924).  They  were  again  cut  in  1921  and 
1922  to  determine  the  fluctuation  from  year  to  year.  The  first  step  in  the 
simple  procedure  was  to  select  a  considerable  number  of  quadrats  in  typical 
areas  of  each  climax.  The  height  and  density  of  the  cover,  the  abundance 
of  dominant  and  subdominant  species,  the  presence  of  layers,  etc.,  were 
recorded  and  photographs  made  of  certain  of  the  quadrats.  In  some 
instances  it  has  proved  desirable  to  make  a  chart  of  these  as  well.  The 
cover  was  then  removed  by  cutting  it  near  the  surface  and  at  a  uniform 
level  with  a  hand-clipper.  It  was  collected,  sorted,  and  then  shipped  into 
the  laboratory  to  be  thoroughly  air-dried,  after  which  the  actual  production 
was  determined  on  the  basis  of  the  dry  weight.  This  gave  an  expression 
of  the  growth  of  the  community  as  a  unit,  as  well  as  the  role  taken  by  each 
dominant  or  subdominant  in  this.  As  complete  factor  records  were  obtained 
at  each  station,  this  made  it  possible  to  correlate  the  yield  of  community  or 
species  with  the  climate  and  the  season  at  each  (plate  10b). 

Since  even  the  most  uniform  cover  shows  some  variation  in  density,  the 
clip-quadrats  were  selected  with  much  care  and  in  sufficient  number  to 
insure  dependable  results.  As  in  all  ecological  studies  that  are  adequate, 
i.  e.,  causal  and  quantitative  rather  than  merely  mathematical,  this  demands 
considerable  knowledge  of  the  community  and  can  not  be  met  by  random 
selection.  The  best  plan  is  to  locate  a  proper  proportion  of  quadrats  in 


86 


RELATED  APPLICATIONS. 


pure  or  nearly  pure  stands  of  each  dominant  whenever  these  are  present 
and  to  distribute  the  others  among  the  various  mixtures.  It  is  often  desir¬ 
able  to  take  the  subdominants  into  account  in  doing  this,  as  their  yield  may 
be  much  greater  than  that  of  the  grasses. 

Results  at  Grassland  Stations. 

In  every  case  each  grass  or  mixture  of  grasses  yielded  progressively  less 
as  the  rainfall  and  holard  decreased  to  the  westward.  The  only  exception 
is  the  case  of  buffalo-grass  at  Lincoln  in  1921,  and  this  is  readily  explained 


Table  6. — Average  yield  of  clip-quadrats ,  in  grams. 


Dominant  type 
of  vegetation. 

1920. 

1921. 

1922. 

Lin¬ 

coln. 

Phil¬ 

lips¬ 

burg. 

Bur¬ 

ling¬ 

ton. 

Lin¬ 

coln. 

Phil¬ 

lips¬ 

burg. 

Bur¬ 

ling¬ 

ton. 

Lin¬ 

coln. 

Phil¬ 

lips¬ 

burg. 

Bur¬ 

ling¬ 

ton. 

Buffalo-grass.  .  . 
Wheat-grass.  .  .  . 
Mixed  short  and 
tall  grasses .  .  . 

290 

541 

313 

410 

98 

500 

197 

235 

606 

266 

457 

207 

400 

541 

260 

334 

365 

287 

179 

263 

Mixed  tail- 

grasses  . 

Average,  based 
on  number  of 
quadrats . 

i 

458 

755 

477 

413 

458 

378 

183 

603 

402 

353 

447 

311 

224 

as  an  effect  of  grazing.  Moreover,  the  averages  for  each  year  at  the  several 
stations  show  a  graduated  series,  plant  production  increasing  with  increased 
efficiency  of  rainfall.  However,  it  may  be  readily  seen  that  the  total  yield 
at  all  of  the  stations  was  greater  in  1921  than  during  the  preceding  or  fol¬ 
lowing  year,  an  increase  particularly  noticeable  in  the  case  of  the  late- 
maturing  tail-grasses  (table  6). 

There  was  a  pronounced  decrease  in  the  height  of  all  three  species  from 
Lincoln  westward,  the  plants  at  Burlington  averaging  less  than  half  as  tall 
as  at  Lincoln.  With  respect  to  weight,  the  differences  were  even  greater, 
oats  and  wheat  yielding  a  third  as  much  as  at  Lincoln.  The  average  pro¬ 
duction  for  the  three  crops  was  2,234  at  Lincoln,  1,164  at  Phillipsburg,  and 
882  at  Burlington,  in  close  correspondence  with  rainfall,  evaporation,  and 
chresard  (table  7). 

Results  in  Grazing  Exclosures. 

Experimental  exclosures  were  installed  in  three  representative  areas  of 
northern  Arizona  in  1918  in  cooperation  with  the  Biological  Survey  of  the 
United  States  Department  of  Agriculture  (Taylor  and  Loftfield,  1922, 
1923).  While  these  were  designed  to  serve  several  purposes,  the  most 
important  was  to  evaluate  the  role  of  grazing  in  the  structure  and  yield  of 
grassland  and  to  determine  the  effect  of  the  food-habits  of  the  prairie-dog 
of  the  region  ( Cynomys  gunnisoni  zuniensis )  upon  the  carrying  capacity 
and  composition  of  the  range.  The  latter  is  a  portion  of  the  mixed-prairie 
association,  usually  modified  in  this  region  by  the  suppression  of  the  tall- 


CLIP-QUADRAT  PHYTOMETERS. 


87 


grasses  through  overgrazing.  The  northern  area  lies  in  Coconino  Wash, 
about  9  miles  south  of  the  Grand  Canyon,  and  consists  of  Agropyrum 
glaucum  and  Sporobolus  cryptandrus,  with  small  amounts  of  Bouteloua 
gracilis,  Stipa  comata,  and  other  grasses.  The  exclosure  consists  of  two 
equal  parts,  proof  against  both  cattle  and  rodents,  but  with  one  containing 
a  group  of  prairie-dogs,  and  it  lies  beside  an  unfenced  area  provided  with 
quadrats  also.  This  series  has  permitted  a  quantitative  study  of  the  vege¬ 
tation  under  three  conditions:  (1)  under  total  protection,  (2)  grazed  by 


Table  7. — Growth  and  yield  of  crop-quadrats ,  1923. 


Crop  and  station. 

Date  of 
harvest. 

Height. 

Weight. 

Oats: 

in. 

gm. 

Lincoln . 

July  7 

42 

2,637.0 

Phillipsburg . 

July  3 

32 

905.0 

Burlington . 

July  7 

18 

806.5 

Wheat : 

Lincoln . 

July  7 

42 

2,395.0 

Phillipsburg . 

July  3 

29 

1,296.0 

Burlington . . 

July  7 

24 

801.5 

Barley: 

Lincoln . 

July  2 

43 

1,671.5 

Phillipsburg .  .  . '. . 

July  3 

37 

1,292.5 

Burlington . 

July  7 

26 

1,038.5 

cattle  alone,  and  (3)  grazed  by  a  known  number  of  prairie-dogs.  Similar 
exclosures  are  located  at  Williams  and  at  Seligman,  the  former  in  a  com¬ 
munity  of  Bouteloua  gracilis  and  Muhlenbergia  gracillima,  the  latter  in  one 
of  B.  gracilis  and  eriopoda. 

Table  8. 


Agropyrum  glaucum. 

Sporobolus  cryptandrus. 

Total  quantity  of  grass. 

1919. 

1920. 

1921. 

1919. 

1920. 

1921. 

1919. 

1920. 

1921. 

Total  protection 

100.0 

117.1 

138.8 

164.6 

32.8 

81.9 

264.6 

149.9 

220.7 

Rodent  grazing. 
Cattle  and  ro- 

36.8 

24.3 

22.6 

Trace. 

None. 

None. 

36.8 

24.3 

22.6 

dent  grazing. .  . 

6.6 

8.7 

6.7 

4.6 

None. 

6.4 

11.2 

8.7 

13.1 

The  growth  of  the  grasses  under  the  three  conditions  has  been  measured 
by  means  of  clip-quadrats,  and  at  the  Coconino  station  has  yielded  the 
figures  presented  in  table  8,  expressed  as  grams  of  forage  per  square  meter: 

Agropyrum  glaucum  shows  a  consistent  increase  for  the  three  years  of 
total  protection,  probably  owing  to  its  better  utilization  of  rainfall  as  a 
result  of  its  sod  habit  (plate  11a).  As  a  bunch-grass,  Sporobolus  cryp¬ 
tandrus  appears  to  be  more  dependent  upon  the  seasonal  distribution  of  the 
rainfall,  and  it  is  also  unable  to  hold  its  own  in  competition  with  the  increas¬ 
ing  Agropyrum.  Rodents  are  especially  fond  of  it,  as  are  cattle  also;  but 
while  the  latter  merely  graze  it  to  the  ground,  the  prairie-dogs  destroy  it 
completely  by  the  second  year. 


88 


RELATED  APPLICATIONS. 


TRANSPLANT  PHYTOMETERS. 

Species  Phytometers. 

As  the  basic  method  in  the  ecological  organization  of  the  field  of  experi¬ 
mental  evolution  (Clements  and  Hall,  1918-1923;  Clements  and  Clements, 
1923)  and  in  the  development  of  the  new  field  of  experimental  vegetation 
(Clements  and  Weaver,  1918-1923,  1924),  transplant  gardens  and  areas 
have  been  installed  in  a  number  of  climatic  and  edaphic  series  in  the  West. 
The  climatic  transect  in  the  grassland  extends  from  Nebraska  City  in  the 
subclimax  prairie  with  a  rainfall  of  33  inches,  to  Lincoln  in  the  true  prairie 
with  28  inches,  Phillipsburg  in  mixed  prairie  with  23  inches,  and  Burlington 
and  Colorado  Springs  in  varying  types  of  mixed  prairie  and  short-grass 
plains  with  a  rainfall  of  17  and  15  inches  respectively.  The  edaphic  tran¬ 
sect  at  Lincoln  runs  through  swamp,  salt-flat,  low  prairie,  high  prairie,  and 
gravel-knoll  in  the  true-prairie  climax  and  climate.  The  Petran  transect 
at  Pike’s  Peak  extends  from  mixed  prairie  with  a  15-inch  rainfall  at 
Colorado  Springs  through  successive  zones  of  montane,  subalpine,  and 
alpine  climaxes  to  a  rainfall  of  30  inches  on  the  summit  of  the  Peak,  while 
the  Sierran  transect  reaches  from  the  Pacific  Ocean  to  the  summit  of  the 
Sierra  Nevada  and  the  sagebrush  desert  of  the  Great  Basin.  Edaphic 
transects  have  also  been  installed  in  various  climates  in  these  two  major 
climatic  series,  but  have  been  especially  developed  at  the  Alpine  Laboratory 
and  at  Mather  in  the  Hetch-Hetchy  Valley.  In  addition  to  these,  adapta¬ 
tion  or  ecad  sequences  of  flowering  plants  have  been  developed  in  varying 
amounts  of  water-content  or  light,  and  similar  sequences  have  been  estab¬ 
lished  for  fungi  and  lichens,  mosses,  etc. 

Practically  all  transplant  installations  have  been  designed  to  serve  a 
dual  purpose,  namely,  plant  response  and  factor  measurement.  In  the 
mountain  transects,  evolution  has  so  far  been  the  primary  objective  and 
habitat  analysis  the  secondary,  while  in  the  grassland  series  measurement 
of  climate  and  climax  has  been  paramount  and  adaptation  secondary. 
However,  both  have  been  constantly  kept  in  mind  as  reciprocals  in  the  com¬ 
plete  synthesis  of  plant  and  habitat.  While  these  are  an  intrinsic  part  of 
the  comprehensive  phytometer  method,  the  detailed  account  is  necessarily 
left  for  the  respective  treatments  (cf.  Clements  and  Weaver,  1924). 

Community  Phytometers. 

The  development  of  community  transplants  as  phytometers  has  neces¬ 
sarily  been  slower,  because  of  the  difficulties  involved,  especially  those  of 
transportation.  These  are  most  readily  solved  in  the  case  of  sod-cores  or 
blocks,  but  the  latter  are  too  small  for  many  of  the  phytometric  values 
cnncrht.  In  the  case  of  exclosures  and  inclosures,  community  phytometers  of 
practically  any  desired  size  are  possible,  but  these  are  limited  to  measure¬ 
ments  of  the  effect  of  grazing  or  other  animals  (plate  11b).  A  further  type 
of  community  phytometer  with  essentially  the  value  of  transplanting  is 
obtained  by  modifying  the  holard  through  irrigating,  flooding,  or  draining, 
or  changing  the  light  intensity  by  thinning,  clearing,  or  producing  an 
artificial  canopy  or  shade.  In  practice,  however,  community  phytometers 
have  been  confined  largely  to  grassland  and  to  lichens  and  mosses.  In  the 


RESUME. 


89 


case  of  the  latter,  entire  communities  are  moved  with  the  greatest  readiness, 
but  with  sod  or  turf  only  fragments  can  be  transported  as  a  rule.  The  most 
feasible  method  of  doing  this  is  to  cut  a  meter  quadrat  into  four  parts, 
which  are  then  readily  moved  if  the  soil-blocks  are  not  too  thick.  Areas 
several  meters  square  have  been  transferred  in  this  way  from  the  alpine 
meadow  to  the  montane  climax.  The  simplest  and  most  successful  device 
for  transplanting  a  community  has  been  that  of  the  reciprocal  transplant 
quadrat,  in  which  the  central  portions  of  two  permanent  quadrats  are 
interchanged  (Clements  and  Loftfield,  1923). 

In  addition  to  the  experimental  transfers  employed  as  phytometers  are 
the  large  number  of  natural  communities  of  definite  limits,  which  occur  as 
pioneers  or  relicts.  These  have  the  advantage  of  requiring  no  installation, 
but  they  are  correspondingly  less  amenable  to  control.  Their  utilization 
as  definite  experiments  under  instrumental  conditions  has  just  been  begun 
and  the  range  of  their  usefulness  is  yet  to  be  determined. 

RESUM  E. 

Values  and  Limitations  of  the  Phytometer  Method. 

The  six  years  of  experience  with  the  phytometer  method  in  a  wide  variety 
of  forms  and  applications  seem  to  justify  the  conclusion  that  it  is  indis¬ 
pensable  to  all  quantitative  studies.  Its  sole  limitation  is  the  labor  and 
expense  involved,  and  this  applies  only  to  growth  phytometers  carried  out 
on  a  large  scale  for  the  entire  season.  Even  with  these,  when  growth  is 
expressed  in  yield  or  dry  weight  for  the  whole  season,  the  operation  is  within 
the  capacity  of  a  single  investigator,  and  this  is  still  truer  of  short-period 
phytometers  utilizing  a  simple  function,  such  as  transpiration.  Moreover, 
it  is  an  advantage  rather  than  a  limitation  that  phytometric  studies  must 
be  carried  through  several  seasons  to  obtain  representative  results,  in  so  far 
as  climate  is  concerned,  a  fact  that  applies  with  equal  force  to  instrumental 
measurements  as  well.  This  is  true  also  of  edaphic  applications,  since  local 
habitats  vary  with  the  seasonal  swing.  In  spite  of  this,  installations  of 
phytometers  for  a  single  season  have  a  wide  range  of  usefulness  whenever 
comparative  values  are  sought  independently  of  the  annual  variations. 
While  the  best  use  of  phytometers  is  in  conjunction  with  instruments,  they 
render  recording  instruments  necessary  only  in  the  more  extensive  instal¬ 
lations.  In  fact,  it  is  to  be  expected  that  the  increasing  standardization  of 
phytometers  will  cause  them  to  largely  replace  the  less  satisfactory  instru¬ 
ments,  such  as  the  atmometer  in  its  various  forms. 

It  seems  unnecessary  to  recapitulate  the  many  uses  of  the  various  kinds 
of  phytometers,  but  it  is  desirable  to  emphasize  the  leading  role  played  by 
the  phytometer  in  the  exact  analysis  of  the  processes  and  changes  of 
vegetation  and  crops.  The  plant  or  community  alone  can  measure  the 
factor-complex,  as  well  as  the  efficient  factors  in  it  and  the  effect  of  their 
annual  fluctuation.  They  are  the  only  measures  of  the  decisive  part  played 
by  competition,  and  of  the  far-reaching  effect  of  animal  reactions  upon 
vegetation.  Finally,  it  is  only  by  the  exact  evaluation  of  the  control 
exerted  by  factor,  competition,  and  animals  that  it  becomes  possible  to 
distinguish  present  and  past  effects  in  vegetation. 


TABLES. 


Table  9. — Results  from  sealed  phytometers,  1918. 
First  Series. 


Ave.  water  re¬ 

quirement. 

Rel.  water  require¬ 

ment. 

Leaf  area,  sq.  dm. 

Transpiration  per 

sq.  dm. 

Ave.  transpiration 

per  sq.  dm. 

Rel.  transpiration 

per  sq.  dm. 

Relative  dry  weight. 

gm. 

2.35 

2.65 

2.89 

2.73 
2.31 
2.89 
2.89 

2.74 
2.71 
7.43 
8.84 

gm. 

396.6 
363 

353.6 

390.7 

215.2 

279.8 
283.7 

260.9 

281.9 

408.2 
238.6 

gm. 

518 

100 

376 

100 

100 

370 

71 

264.3 

70 

101 

542 

365 

765 

100 

67 

100 

408.2 

238.6 

100 

58 

100 

103 

100 

65 

509 

66 

766 

100 

100 

91 

657 

86 

Station. 


Plains 
Do.  . 
Do.  . 
Do.  . 
Montane . 
Do.  . 
Do.  . 
Do.  . 
Do.  . 
Plains 
Montane . 
Plains. . . . 

Do.  . 
Montane . 
Do.  . 
Do.  . 
Do.  . 
Do.  . 
Plains 
Montane . 
Do.  . 


Species. 


Sunflower. 
. . .  Do .  .  . 

. .  .  Do .  .  . 
...  Do .  .  . 
...  Do.  .  . 
...  Do.  .  . 
. .  .Do.  .  . 

. . . .  Do .  .  . 

.  . .  .Do.  .  . 
Beans. . .  . 
. . .  .Do.  .  . 

Oats . 

. . .  .Do.  .  . 
. . . .  Do .  .  . 
. . .  .Do.  .  . 
. . . .  Do .  .  . 
. . . .  Do .  .  . 
.  . .  .Do.  .  . 
Wheat.  .  . 
. . . .  Do .  .  . 
. . . .  Do .  .  . 


CO 

cS 

oq 

6 

Z 


1 

1 

1 

1 

1 

1 

1 

1 

1 

6 

6 

6 

4 

8 

4 

6 

6 

4 

5 
4 

10 


"O 

© 

<U 

P 

l-i 

© 

S3 

£ 

*o3 

-t^> 

O 


gm. 
932 
962 
1,022 
1,066.5 
497 
808.6 
820 
714.8 
764 
3,033 
2,109 
384 
367 
218 
104 
177 

281.5 

130.5 
295 
210.7 

384.5 


xi 

•  ^ 
© 

* 

b 


gm. 

1.673 

1.930 

2.185 

1.947 

1.324 

2.103 

2.234 

1.966 

2.132 

5.593 

5.776 

.530 

.452 

.456 

.225 

.286 

.515 

.296 

.385 

.276 

.699 


i 

© 

.« 

P 

c 

© 

i ■* 


*2 
u  p 
©  © 

*  B 
£ 


gm. 

557 

498 

468 

548 

375 

384 

367 

364 
358 
542 

365 
725 
812 
478 
462 


441 


Second  Series. 


Plains. . . . 

Do.  . 
Montane . 

Do.  . 
Plains. . . . 

Do.  . 
Montane . 

Do.  . 
Plains 
Do.  . 
Montane . 

Do.  . 
Plains 


Montane . 
Do.  . 
Do.  . 


Sunflower 
. .  .Do.  . 
...  Do .  . 

. .  .Do.  . 
Oats. . . . 

. .  .Do.  . 
...  Do .  . 

.  . .  .  Do .  . 
Wheat.  . 
...  Do .  . 

.  ...Do.  . 

. . .  .Do.  . 
Sweet 
clover. 
....Do.  . 
....Do.  . 

.  . . .  Do .  . 


1 

1 

1 

1 

20 

13 
27 
26 

9 

14 
23 
20 

5 

4 

5 
3 


gm. 
4,124 
4,018 
2,468 
2,432 
1,677 
1,012 
1,512 
1,312 
1,014 
784 
1,537 
1,190 
510 


5 


.5 

.5 

.5 


130.5 
175 
239 


gm. 
10.873 
10.439 
8.273 
8.988 
3 . 533 
1.699 
5.283 
3.417 
1.753 
1.900 
4.672 
3.842 
.965 

.511 

.590 

.684 


gm. 

379 

384 

298 

271 

475 

596 

286 

384 

578 

394 

329 

310 

529 

255 

297 

349 


gm. 

382 

100 

285 

74 

536 

100 

335 

63 

486 

100 

320 

66 

529 

100 

.  300 

57 

7.70 

8.37 

9.90 

9.56 

5.85 

2.26 

10.69 

7.19 

1.95 

2.97 

7.25 

6.53 

gm. 

535.6 
480 

249.3 

254.4 

286.7 

447.8 

141.5 

182.5 
520 

251.9 
212.1 
182.3 

gm. 

507.8 

100 

100 

251.9 

50 

81 

100 

367.3 

100 

162 

44 

166 

100 

386 

100 

197.2 

51 

230 

100 

62 

90 


TABLES 


91 


Table  9. — Results  from  sealed  phytometers,  1918 — Continued. 


Third  Series. 


Station. 

Species. 

No.  stalks. 

Total  water  used. 

Dry  weight. 

Water  require¬ 

ment. 

Ave.  water  re¬ 

quirement. 

Rel.  water  require¬ 

ment. 

Leaf-area,  sq.  dm. 

Transpiration  per 

sq.  dm. 

Ave.  transpiration 

per  sq.  dm. 

!  Rel.  transpiration 

per  sq.  dm. 

Relative  dry  weight. 

gm. 

gm. 

gm. 

gm. 

gm. 

gm. 

Plains . 

Sunflower. . 

1 

1  873 

1  734 

1,080 

1  98 

946 

Do.  .  .  . 

....  Do .... 

1 

1  869 

1  557 

1  200 

1,140 

100 

1  88 

994  1 

970.1 

100 

100 

Montane .  .  . 

1 

935  5 

2  654 

352 

3  16 

296 

Do.  .  .  . 

....  Do .... 

1 

954  2 

3  037 

314 

3  07 

310.8 

Do ... . 

.  .  .  .Do.  .  .  . 

1 

811  2 

1  806 

449 

372 

33 

2  52 

321  9 

309.6 

32 

152 

Gravel-slide . 

1 

709 

1  496 

474 

2  64 

268.6 

Do.  .  .  . 

. .  .  .Do.  .  .  . 

1 

1  170 

2.393 

489 

3  35 

349.3 

Do.  .  .  . 

....  Do .... 

1 

978 

1  945 

503 

489 

43 

2  84 

344.4 

320.8 

33 

118 

Douglas  fir. . 

1 

74 

306 

242 

62 

119.4 

Do.  .  .  . 

1 

110 

.318 

346 

74 

148.6 

Do ... . 

_ Do _ 

1 

115 

307 

375 

321 

28 

73 

157.5 

141  8 

15 

19 

Spruce . 

1 

164 

.419 

391 

72 

227.8 

Do.  .  .  . 

....  Do .... 

1 

74  5 

309 

241 

316 

27 

67 

111  2 

169.5 

17 

22 

Plains . 

Oats . 

6 

885 

953 

929 

1  57 

563  7 

Do.  .  .  . 

....  Do .... 

6 

1,174 

1  370 

857 

893 

100 

2  57 

456  8 

510.3 

100 

100 

Montane .  .  . 

. . .  .Do.  .  .  . 

6 

501.1 

.840 

597 

1  31 

382.5 

Do.  .  .  . 

....  Do .... 

6 

500  2 

1  057 

473 

535 

60 

1  74 

287  5 

335 

66 

82 

Gravel-slide. 

5 

412.5 

.843 

489 

1  24 

332.7 

Do.  .  .  . 

. . .  .Do.  .  .  . 

4 

360.5 

.527 

684 

1  01 

356.9 

Do.  .  .  . 

....  Do .... 

4 

431  2 

.781 

552 

575 

64 

9 

479  1 

389.6 

76 

62 

Douglas  fir. . 

3 

20.2 

.102 

198 

16 

33.6 

Do.  .  .  . 

_ Do _ 

4 

23 

.203 

113 

156 

17 

1.00 

23 

28.3 

6 

13 

Spruce . 

....  Do .... 

4 

85 

271 

314 

1  24 

68.5 

Do ... . 

....  Do .  .  .  . 

3 

60.4 

.185 

326 

320 

36 

87 

69.4 

69 

14 

20 

Plains . 

Rubus .... 

1 

721 

1.91 

377.5 

Do.  .  .  . 

....  Do .... 

1 

856.5 

1.78 

481.2 

Do.  .  .  . 

....  Do .  .  .  . 

1 

863.5 

2.51 

344 

400.9 

100 

Montane.  .  . 

.  . .  .Do.  .  .  . 

1 

252.5 

1.09 

231.7 

Do.  .  .  . 

....  Do .  .  .  . 

1 

295.8 

1.18 

250.7 

Do ... . 

....  Do .  .  .  . 

1 

152.5 

.73 

208.9 

230.4 

57 

Gravel-slide. 

1 

318 

1.29 

246.5 

Do.  .  .  . 

....  Do .  .  .  . 

1 

259.5 

.75 

346 

Do ... . 

....  Do .  .  .  . 

1 

83 

.54 

153.7 

248.7 

62 

Douglas  fir. . 

....  Do .  .  .  . 

1 

33 

.80 

41.3 

Do.  .  .  . 

....  Do .  .  .  . 

1 

96.5 

1.02 

94.6 

Do.  .  .  . 

....  Do .  .  .  . 

1 

45 

.77 

58.4 

64.8 

16 

.... 

Spruce . 

....  Do .  .  . . 

1 

46 

.42 

109.5 

,  (  . 

Do ... . 

....  Do .  .  .  . 

1 

63.7 

.69 

92.3 

Do.  .  .  . 

....  Do .  .  .  . 

1 

50.5 

.50 

90.2 

97.3 

24 

Table  10. — Summary  of  sealed  j)hytometers,  1918. 


92 


THE  PHYTOMETER  METHOD. 


•  ® 

°  «? 

£ 


NOiOiONSNNNCCM 

CMCM-tf-^eocoooooeocMCM 


NNNNNNN*0|0NNO‘0(N(NNMN 

cocococococococmcmcoco^^cococococo 


T3 

o 

•  Pi 
>1 
© 


O  O  CM 

: 

co 

o 

CM 

• 

CO 

o 

CM 

CM 

H  H  CM 

• 

rH 

rH 

CM 

• 

H 

rH 

CM 

• 

CM 

>>>>>> 

. 

db 

>> 

>> 

; 

db 

>3 

. 

>s 

3  3  3 

d 

3 

d 

• 

d 

33 

d 

• 

d 

>“9  >~3  >“S 

. 

<5 

•< 

o  o  o 

• 

r> 

o 

o 

• 

n 

O 

o 

• 

o 

-H  H-> 

• 

• 

• 

CO  T*H  T*< 

o 

o 

c 

c 

c 

c 

Q  c 

o  o 

iO 

rH 

o 

o 

c 

c 

c 

c 

iO 

r-f  C 

o 

rH 

o 

t> 

©  ©  © 

G 

C 

Q  Q  Q  ©  Q  Q  Q 

© 

Q 

Q 

Q  Q  Q  ©  Q 

© 

Q 

© 

d  d  d 

•  • 

d 

d 

r*i 

• 

d 

d 

• 

d 

d  d  d 

d 

• 

d 

d 

• 

d 

d 

d 

• 

d 

>“S  C-5  H-j 

. 

♦“D 

. 

►"5 

. 

. 

. 

►"D 

*"3 

co 


60 

d 

<1 

o 


o  o  o  o 

QQQQ 


d 

*-5 


© 

pH 


I 

c3 
(-1 
•  rH 

a 

03 

d 

c3 

►H  ^ 


©  Q 

ft  a 
*d 
d  • 
o  cr 


©OOOOCMCO*Ot^O 

ONOiOOWMHHO 


co 

lO 


O^OCtDtD't 
OifOQN  «-t 


O 

o  o 


O  CM  CO 
O  »C  CD  H  N 


i 

o3  m  • 
,  ©  q 

®  ft  a| 

^  go  <* 


etO^XNOOHiMOOOOi 

ENOOiONHNrfNOM 

amC5iONOCCCMHHTj((N 


MNOiOOQO® 
CO  CO  H  CC  ®  (N  CD 

co  *h  >o  co  co 


CO  b- 

oo  ca 

CO  r-t 


HO®»ON 
O  C3  M'  CO  03 
^  CM  CM 


03  «JL 
>  C3  ® 
G8 


^COHNCOCOCN’fOOTfiN 

r«C0l>OI>0Ci0303l>l>iM'^ 


lO  ^  1C  »£>  Tj<  l>  o 

<M  CO  CO  CM  <N  *H  CO 


i-i  CM 
CM  CO 


N  O  CO  CD  CD 
O  O  00  00  id 


^  CM  CM  00  03 

03 


CM  CM 


CM 


© 

« 


i 

0)  • 

s.  § 

&  a 


OHO^OMCOaXONOOOCOOOICNCOOcOOcOON 

ONONOCOifC'KNOCOOCOOCOOCOCOHCOOMOcOOiO 

rH  r-H  r— H  r-H  r— H  rH  rH  r-H  r-H  ^ 


I 

03 


.  M 

©  0) 

^  S  g*  a 


*-<  d 

© 


.OCOCMiCOCM03CMCOCMiOiOC3COiOC®»OiOCOOOI>CDOOiO 

eHNOCOO^NCOOH^OcOOCOCOOSCONiOCMCOiOOOCMCMO 

^lOCOmCMiHCO^COMiOCONiOiOCOOOiOiOHCONCOTHCOiOCO 


+3 

£  «) 
T3  03 
£ 


s 

Os 


TtdMCDHC003i0O^CMC000rH03^TjC003CTjci0NO03  00  C003 
COiOiOCOrtCOS^HCOCOCOOSCOiOCOOiOCO^CONNlOOO)^ 
05  05  CO  CD  CO  05  CO  CO  05  05  O  O  *"H  rH  rH  rH  rH  O  O  O  O  *“H  -H  r-H  r-H 


rH  r-H  O  GO  *"H  Cl  r-H 


QQ 

6^ 

Z  $ 

33 


-tfiOCMCMCMCOCOCOCMCOCOOOOCOCOCMCM 

»— i  CM  CO  *0  i— l  tH 


CO  N  N 


lOHCOCOtOCMCOCOCO 
rH  CM  ^  1-1 


co 


•  ® 
O  -u 
£  O 
^  ft 


■^lOCMCMCMCOCOCOCMCOCOCMiOCMCMCMCMCOCMCMHCMCMCMrHCOCOCOCO 


CO 


33 

03 

•  r- 

t- 

03 

in 


Hr-tC'lCMCOCOCOCOCOHrHHHCMCMCOCOCOCOCOHHCMCMCMCMCOCOCO 


CO 


33 
© 
•  rH 
© 
© 
ft 

in 


u 

© 
p£ 

oOOOOOOOO 

cCQQQQQQPQ 
c 
d 

m 


Sh 

© 

> 

o 


O  ’OOOOOOOO 

QmQQQQQQQQ 

-M 

03 


O  O 

QQ 


o 

Q 


m 

d 

-Q 

d 

Ph 


o  o  o  o 

QQQQ 


d 

o 

•  i-i 

H-a 

cC 

CO 


■o  n 

©'t3® 


•  ©  •  ©  •  ©  -=$  _ 
•  o  •  o  ■  q  f  ® 

.3  c.h  si  fl  c  q 


"S)  I  S 


© 

d 

csj 


© 

d 


© 


03  ^  ^ 


TABLES 


93 


Table  11. — Results  from  unsealed  phytometers,  1918. 


Second  Series. 


Station. 

Species. 

No.  of 
pots. 

No.  of 
plants. 

Leaf- 

area. 

Dry 

weight. 

Ave. 

leaf-area. 

Ave.  dry 
weight. 

Rel.  dry 
weight. 

sq.  dm. 

sq.  dm. 

gm. 

Plains . 

Sunflower. .  .  . 

3 

3 

6.25 

7.573 

2.08 

2.524 

Montane . 

_ Do . 

2 

2 

5.51 

5.674 

2.76 

2.837 

81 

Plains . 

Beans . 

5 

5 

9.29 

4.898 

1.86 

.98 

Montane . 

_ Do. . 

4 

4 

4.27 

2.455 

1.07 

.61 

62 

Plains . 

Oats . 

5 

48 

7.477 

.  156 

Montane . 

_ Do . 

6 

40 

5.468 

.137 

88 

Plains . 

Wheat . 

3 

44 

9.361 

.213 

Montane . 

_ Do . 

3 

36 

4.134 

.115 

54 

Third 

Series. 

sq.  dm. 

sq.  dm. 

gm. 

Plains . 

Sunflower. .  .  . 

5 

5 

12.09 

9.274 

2.42 

1.855 

100 

Montane . 

_ Do . 

5 

5 

12.29 

8.610 

2.46 

1.722 

93 

Gravel-slide. .  .  . 

_ Do . 

5 

5 

6.87 

4.440 

1.37 

.888 

48 

Douglas  fir ...  . 

_ Do . 

2 

2 

1.29 

.240 

.65 

.120 

7 

Spruee . 

_ Do . 

3 

3 

.86 

.475 

.29 

.158 

9 

Plains  . 

Oats . 

5 

93 

9.277 

.100 

100 

M nn  tan e . 

_ Do . 

5 

82 

10.806 

.132 

132 

Gravel-slide.  .  . 

_ Do . 

5 

74 

8.690 

.117 

117 

Douglas  fir  .  .  . 

_ Do . 

5 

90 

3.742 

.042 

42 

Snrnee 

_ Do . 

5 

79 

4.364 

.055 

55 

Table  12. — Summary  of  unsealed  phytometers,  1918. 


Station. 

Species. 

Series. 

No. 

of 

pots. 

No. 

of 

stalks. 

Ave. 

dry 

weight. 

Ave. 

leaf- 

area. 

r 

Period. 

No. 

days. 

gm. 

sq.  dm. 

Plains . 

Sunflower. . 

2 

3 

3 

2.524 

2.08 

June  12  to  July  22 

40 

IVTnnt.ane 

.  Do.  .  .  . 

2 

2 

2 

2.837 

2.76 

....  Do . 

40 

Plains . 

....  Do .... 

3 

5 

5 

1.855 

2.42 

July  10  to  Aug.  16 

35 

\Tnntane 

Do  .  . 

3 

5 

5 

1 .722 

2.46 

_ Do . 

35 

Grn  vel-slide 

Do  .  .  . 

3 

5 

5 

.888 

1.37 

_ Do . 

35 

Dmi  crl  a  .a  fir. 

Do.  .  . 

3 

2 

2 

.120 

.65 

.  .  .  .Do . 

35 

Snrnee 

_ Do.  .  .  . 

3 

3 

3 

.158 

.29 

.  .  .  .Do . 

35 

Plains 

Oats . 

2 

5 

48 

.556 

June  24  to  July  22 

28 

Do 

2 

6 

40 

.137 

_ Do . ' _ 

28 

PI  a  i  n  s 

_ Do ...  . 

3 

5 

93 

.100 

July  10  to  Aug.  16 

35 

Do 

3 

5 

82 

.  132 

.  .  .  ~Do . 

35 

Do 

3 

5 

74 

.117 

_ Do . 

35 

Dmi 0*1  n s  fir 

Do 

3 

5 

90 

.042 

_ Do . 

35 

£srkrnr*p* 

Do 

3 

5 

79 

.055 

_ Do . 

35 

Plains 

Beans . 

2 

5 

5 

.980 

1.86 

June  24  to  July  22 

28 

M  nn  t.a  n  e 

Do. 

2 

4 

4 

.610 

1.07 

...  .Do . .  . 

28 

Wheat 

2 

3 

44 

.213 

_ Do . 

28 

Do 

2 

3 

36 

.115 

....  Do . 

28 

94 


THE  PHYTOMETER  METHOD 


Table  13. — Results  from  sealed  phytometers ,  1919. 


First  Series. 


Station. 

Species. 

No.  of  pots. 

Ave.  dry  weight, 
per  plant. 

Ave.  water  re¬ 

quirement. 

Rel.  water  re¬ 

quirement. 

Ave.  leaf-area. 

Ave.  transpira¬ 

tion  per  sq.  dm. 

Rel.  transpira¬ 

tion  per  sq.dm. 

Period. 

Days. 

gm. 

gm. 

sq.dm. 

gm. 

Plains. . . . 

Sunflower 

5 

12 . 653 

401 

100 

7.883 

644 

100 

June  24  to  Aug. 

1 

38 

Do.  .  . 

Wheat.  .  . 

5 

1.606 

557 

100 

2.146 

384 

100 

....  Do . 

38 

Do .  .  . 

Oats . 

3 

1.252 

567 

100 

2.008 

354 

100 

_ Do . 

38 

Do.  .  . 

Beans. . . . 

5 

5.803 

665 

100 

8.977 

430 

100 

June  26  to  Aug. 

1 

36 

Montane . 

Sunflower 

5 

6.444 

352 

87 

5.330 

420 

65 

June  27  to  Aug. 

1 

35 

Do.  .  . 

Wheat.  .  . 

5 

2.573 

351 

68 

3.981 

226 

58 

June  24  to  Aug. 

1 

38 

Do.  .  . 

Oats . 

5 

1.724 

342 

59 

3 . 660 

158 

44 

....  Do . 

38 

Do.  .  . 

Beans. . . . 

5 

2.623 

424 

63 

4.429 

251 

58 

June  26  to  Aug. 

1 

36 

Subalpine 

Sunflower 

5 

2.967 

280 

72 

3.741 

230 

35 

June  25  to  Aug. 

1 

37 

Do.  .  . 

Wheat.  .  . 

3 

1.764 

173 

26 

3.07 

78 

20 

....  Do . 

37 

Do .  .  . 

Oats . 

3 

1.632 

249 

43 

3.041 

133 

37 

....  Do . 

37 

Do.  .  . 

Beans .... 

4 

.822 

287 

47 

1.061 

245 

56 

.  . .  .Do . 

37 

Second 

Series. 

gm. 

gm. 

sq.dm. 

gm. 

Plains .... 

Sunflower 

2 

5.806 

669 

100 

4.724 

822 

100 

Aug.  5  to  Sept. 

8 

34 

Do.  .  . 

Wheat.  .  . 

2 

.482 

977 

100 

1.023 

460 

100 

Aug.  14  to  Sept. 

8 

25 

Do.  .  . 

....  Do .  .  . 

2 

1.128 

858 

100 

3.517 

218 

100 

Aug.  5  to  Sept. 

8 

34 

Do.  .  . 

Oats . 

3 

1.739 

778 

100 

3.538 

382 

100 

Aug.  7  to  Sept. 

8 

32 

Montane . 

Sunflower 

3 

2.107 

592 

88 

2.207 

565 

69 

Aug.  6  to  Sept. 

8 

33 

Do.  .  . 

Wheat.  .  . 

3 

.116 

931 

95 

.240 

450 

98 

....  Do . 

33 

Do.  .  . 

....  Do .  .  . 

2 

.542 

644 

75 

.893 

390 

179 

....  Do . 

33 

Do.  .  . 

Oats . 

3 

1.463 

1,075 

138 

3.480 

452 

118 

Aug.  8  to  Sept. 

8 

31 

Subalpine 

Sunflower 

3 

2.177 

513 

77 

2.762 

404 

49 

Aug.  4  to  Sept. 

8 

35 

Do.  .  . 

Wheat .  .  . 

3 

.628 

622 

63 

1.091 

358 

77 

.  .  .  .Do . 

35 

Do.  .  . 

_ Do.  .  . 

2 

1.293 

594 

69 

2.331 

329 

150 

Aug.  11  to  Sept. 

8 

28 

Do.  .  . 

Oats . 

3 

.692 

609 

78 

1.359 

310 

81 

Aug.  9  to  Sept. 

8 

36 

Table  14. — Results  from  sealed  phytometers,  1920. 


Station. 

First  series. 

Second  series. 

Species. 

Aver. 

total 

transpira¬ 

tion. 

Aver. 

dry 

weight. 

Aver. 

water 

require¬ 

ment. 

Aver. 

total 

transpira¬ 

tion. 

Aver. 

dry 

weight 

Aver. 

water 

require¬ 

ment. 

Plains . 

Montane. . .  . 
Subalpine.  .  . 

Plains . 

Montane. . . . 
Subalpine.  .  . 

Plains . 

Montane. . . . 
Subalpine.  .  . 

Sunflower. . .  . 

.  .  .  .Do . 

.  .  .  .Do . 

Wheat . 

.  .  .  .Do . 

.  .  .  .Do . 

Oats . 

...  .Do . 

.  .  .  .Do . 

gm. 

1,734 

1,311 

359 

1,050 

740 

408 

1,529 

965 

497 

gm. 

3.8045 

3.1582 

.829 

1.604 

1.3943 

.7541 

2.7186 

1.8082 

.954 

gm. 

456.30 

415.07 

434.29 

650.99 

530.70 

543.35 

543.35 

532.41 

520.96 

gm. 

2,967 

5,180 

1,465.9 

145.2 

1,108.7 

703.4 

2,356.6 

1,759.5 

566.8 

gm. 

6.7879 

14 . 5083 
3.7213 
.3151 
2.5341 
2.0122 
5.4923 
4.3182 
1.2892 

gm. 

437.10 

357.04 

396.60 

460.8 

437.51 

349 . 56 

429.07 

407.46 

133.74 

TABLES 


95 


Table  15. — Average  stem  length  and  width  of  sunflowers  in  millimeters ,  1920. 


First  Series. 


Station. 

June 

14  to  21. 

June 

21  to  28. 

June  28  to 
July  5. 

July 

5  to  12. 

July 

12  to  19. 

Plains . 

42.6 

63.8 

123.2 

191 

285.4 

Montane . 

16.4 

32.2 

74.4 

132 

212 

Subalpine . 

14 

14.8 

42.6 

62.8 

93 

Plains . 

2.88 

3.12 

4.26 

5.54 

6.80 

Montane  . 

2.42 

2.50 

3.68 

5.56 

7.20 

Subalpine . 

2.55 

2.57 

3.34 

4.18 

5.40 

Second 

Series. 

July 

July  26  to 

Aug. 

Aug. 

Aug. 

Aug. 

Old/llUlL 

19  to  26. 

Aug  2. 

2  to  9. 

9  to  16. 

16  to  23. 

23  to  30. 

Plains . 

16.8 

38.8 

57.2 

87.2 

166.8 

287.4 

Montane . 

17.6 

31.6 

67.6 

115.4 

171.8 

243.6 

Subalpine . 

17.6 

20.6 

35.4 

58 

75.2 

107.6 

Plains . . 

1.76 

2.04 

2.72 

3.2 

4.14 

4.94 

Montane . 

2..  24 

2.50 

3.42 

4.62 

5.82 

7.04 

Subalpine . 

2.46 

2.38 

2.74 

3.52 

4.12 

5.02 

96 


THE  PHYTOMETER  METHOD 


Table  16. — Average  daily  transpiration  of  sunflower  phytometers,  1923. 


First  Series. 


June 
13  to 
18. 

June 
18  to 
25. 

June 
25  to 
July  1. 

July 

1  to 

3. 

July 

3  to 

5. 

July 

5  to 

7. 

July 

7  to 
9. 

July 

9  to 
12. 

July 
12  to 
14. 

Sun  Station: 

Average  daily  water- 
loss  (c.  c.) . 

16.2 

32.37 

32  48 

31  00 

67  50 

85  00 

90  00 

47.90 

85.90 

Average  leaf-area  (sq. 
dm.) . 

0  627 

0.871 

1  511 

1  908 

2  342 

2  777 

2  994 

3  628 

3.959 

Transpiration  per  sq. 
dm . 

25.8 

37.16 

21  49 

16.24 

28.82 

30  60 

30 . 06 

13.20 

21.69 

Half-shade  station: 

Average  daily  water- 
loss  (c.  c.) . 

8  2 

14  7 

11  3 

21  0 

23  8 

33  0 

44  0 

36  2 

42  6 

Average  leaf-area  (sq. 
dm.) . 

0 . 835 

1.026 

1  497 

1  778 

2  092 

2.395 

2.604 

2.872 

3.088 

Transpiration  per  sq. 
dm . 

9  81 

14  32 

7  54 

11  86 

11  37 

15  77 

16  89 

12.60 

13.79 

Shade  station: 

Average  daily  water 
loss  (c.  c.) . 

14.8 

9.95 

9  15 

10  0 

14  3 

20  5 

12  8 

8.98 

8.10 

Average  leaf-area  (sq. 
dm.) . 

0.792 

0.872 

0.999 

1  047 

1  114 

1.181 

1.248 

1.302 

1.327 

Transpiration  per  sq. 
dm . *  . 

20.87 

11.39 

9.15 

9.55 

12.83 

17.36 

10.26 

6.89 

6.10 

Second  Series. 


Aug.  ' 
2  to  6. 

Aug. 

6  to  13. 

Aug. 

13  to  20. 

Aug. 

20  to  27. 

Aug.  27  to 
Sept.  3. 

Sun  station: 

Average  daily  water-loss  (c.  c.) .  .  . 

3.97 

3.60 

2.58 

6.20 

4.96 

Average  leaf-area  (sq.  dm.) . 

34.22 

42.17 

55.92 

65.56 

78.05 

Transpiration  per  sq.  dm . 

11.60 

8.53 

4.61 

9.45 

6.11 

Half-shade  station: 

Average  daily  water-loss  (c.  c.) .  .  . 

1.60 

3.00 

1.50 

2.80 

1.32 

Average  leaf-area  (sq.  dm.) . 

35.24 

41.04 

51.84 

53.99 

49.72 

Transpiration  per  sq.  dm . 

4.54 

7.30 

2.89 

5.18 

2.65 

Shade  station: 

Average  daily  water-loss  (c.  c.) .  .  . 

0.47 

0.91 

0.50 

0.53 

0.40 

Average  leaf-area  (sq.  dm.) . 

31.64 

36.94 

44.96 

50.82 

51.68 

Transpiration  per  sq.  dm . 

1.48 

2.47 

1.11 

1.04 

0.77 

TABLES 


97 


Table  17. — Growth  of  sunflower  phytometers,  1923. 

First  Series. 


j 

Date. 

Sun  station. 

Half-shade  station. 

Shade  station. 

Phyto¬ 

meters. 

Checks. 

Phyto¬ 

meters. 

Checks. 

Phyto- 

meters. 

Checks. 

Average  leaf-area  in  sq.  cm. : 

June  18 . 

62.70 

83.56 

79.20 

June  25 . 

111.55 

100 . 68 

121.71 

104.08 

95.22 

77.87 

July  2 . 

190.82 

174.26 

177.82 

134.06 

104.71 

81.28 

July  9 . 

342 . 99 

274.20 

128.25 

July  13 . 

395.90 

492.41 

308.88 

169.24 

135.20 

96.26 

Average  stem-length  in  mm. : 

June  18 . 

48.2 

72.9 

84 

June  25 . 

82.7 

119 

165.2 

178 

181.5 

187 

July  2 . 

116 

136 

264.6 

230 

244.7 

228 

July  9 . 

180.5 

393 

338.1 

July  13 . 

203.3 

226 

428.2 

330 

304.8 

238 

Average  stem-diameter  in 

mm.: 

June  18 . 

4 

3.80 

3.70 

June  25 . 

3.90 

4.30 

4.20 

4 

3.65 

3.70 

July  2 . 

5.47 

4.60 

5.24 

4.30 

3.91 

3.71 

July  9 . 

6.54 

6  09 

4.02 

July  13 . . 

7.45 

6 

6.64 

4.40 

4.27 

3.70 

Second  Series. 

Average  leaf-area  in  sq.  cm. : 

Aug.  6 . 

34.22 

38.05 

35.24 

40.19 

31.64 

31.37 

Aug.  13 . 

50.13 

46.82 

46.84 

51.79 

42.24 

38.86 

Aug.  20 . 

61.72 

55.51 

56.85 

63.03 

47.69 

45.72 

Aug.  27 . . 

69.40 

69.08 

51.13 

67.28 

53 . 95 

50.09 

Sept.  3 . 

86.71 

96.90 

48.32 

75.09 

59.41 

54.43 

Average  stem-length  in  mm. : 

Aug.  6 . 

88.9 

112.8 

97.8 

128.2 

110.2 

118.3 

Aug.  13 . 

105.5 

130.5 

125.5 

165.5 

156 

160.5 

Aug.  20 . 

117.5 

146.2 

145 

203.5 

180 

195 

Aug.  27 . 

145.5 

137 

162.1 

234 

200.6 

214 

Sept.  3 . 

155.5 

183.5 

169.2 

250.5 

213.7 

257 

Average  stem-diameter  in 

mm.: 

Aug.  6 . 

2.73 

3.09 

2.76 

3.09 

2.70 

2.84 

Aug.  13 . 

3.15 

3.34 

3.20 

3.29 

2.70 

2.87 

Aug.  20 . 

3.31 

3.30 

3.42 

3.28 

2.71 

2.80 

Aug.  27 . 

3.51 

3.54 

3.80 

3.28 

2.68 

2.86 

Sept.  3 . 

3.76 

3.83 

3.28 

3.40 

2.45 

2.75 

98 


THE  PHYTOMETER  METHOD 


Table  18. — Dry  weight  and  water  requirement  of  sunflower  phytometers,  1928. 


First  Series. 


Station. 

Phytometers. 

Checks. 

Ave. 

water 

require¬ 

ment. 

Leaves. 

Stems. 

Roots. 

Plant. 

Leaves. 

Stems. 

Shoot. 

Average  dry  weight  in 
grams: 

Sun . 

Half-shade . 

Shade . 

1.2894 
.  6233 
.1650 

0.6393 

.7750 

.1280 

0.4769 

.3352 

.0614 

2.4056 

1.7335 

.3544 

0.8030 

.3130 

.1390 

0 . 5500 
.4040 
.1106 

1.353 

.7170 

.2496 

804.9 

486.5 

124.91 

Station. 

Leaves. 

Stems. 

Roots. 

Leaves. 

Stems. 

Percentage  of  sun-sta¬ 
tion  values: 

Sun . 

Half-shade . 

Shade . 

100 

48.34 

12.79 

100 

121.24 

20.02 

100 

70.28 

12.83 

100 

38.96 

17.31 

100 

73.45 

20.10 

Second  Series. 

Station. 

Phytometers. 

Checks. 

Ave. 

water 

require¬ 

ment. 

Leaves. 

Stems. 

Roots. 

Plant. 

Leaves. 

Stems. 

Shoot. 

Ave.  dry  weight  in  grams: 

Sun . 

Half-shade . 

Shade . 

0.4589 

.3402 

.1695 

0.3724 

.3694 

.1412 

0.2047 

.2789 

.1024 

1 . 0360 
.9885 
.4131 

0.4792 
.2142 
. 12778 

0.3421 

.1553 

.1293 

0.8213 

.3695 

.2571 

165.1 

94 

58.7 

Station. 

Leaves. 

Stems. 

Roots. 

Leaves. 

Stems. 

Percentage  of  sun-sta¬ 
tion  values: 

Sun . 

Half-shade . 

Shade . 

100 

74.1 

36.9 

100 

99.2 

37.9 

100 

135.2 

50.0 

100 

44.6 

26.6 

100 

45.3 

37.7 

TABLES 


99 


Table  19. — Individual  variability  in  transpiration  of  sunflowers. 

Fibst  Series. 


(Disc.  =  Discarded) 


No. 

Loss  in 
weight. 

Ave.  leaf 
product. 

Loss  per  ave. 
product. 

No. 

Loss  in 
weight. 

Ave.  lead 
product. 

Loss  per  ave. 
leaf  product. 

gm. 

gm. 

gm. 

gm. 

1 

12.6 

2,570 

0.0049 

51 

13.1 

2,609 

0 . 0050 

2 

10.5 

2,556 

.0041 

52 

7.9 

1,263 

.0062 

3 

11.5 

2,328 

.0049 

53 

8.4 

1,274 

.0065 

4 

10.4 

2,773 

.0037 

54 

Disc. 

5 

Disc. 

55 

13.5 

2,877 

.0046 

6 

14.7 

2,575 

.0057 

56 

Disc. 

7 

Disc. 

57 

6.9 

2,952 

.0023 

8 

Disc. 

58 

Disc. 

9 

21.8 

3,451 

.0063 

59 

11.7 

2,430 

.0047 

10 

Disc. 

60 

13.0 

2,450 

.0050 

11 

13.4 

1,943 

.0068 

61 

17.5 

2,536 

.0068 

12 

12.5 

1,998 

.0062 

62 

10.1 

2,084 

.0064 

13 

10.4 

1,768 

.0058 

63 

13.2 

2,594 

.0051 

14 

15.3 

2,739 

.0055 

64 

7.3 

2,097 

.0035 

15 

13.1 

3,120 

.0042 

65 

9.4 

2,069 

.0040 

16 

Disc. 

66 

14.0 

2,916 

.0048 

17 

Disc. 

67 

Disc. 

18 

Disc. 

68 

10.5 

1,867 

.0058 

19 

19.5 

1,899 

.0050 

69 

Disc. 

20 

Disc. 

70 

10.2 

2,219 

.0045 

21 

7.0 

2,073 

.0034 

71 

Disc. 

22 

13.7 

2,053 

.0067 

72 

Disc. 

23 

9.6 

2,689 

.0036 

73 

9.5 

2,538 

.0037 

24 

10.3 

1,708 

.0060 

74 

16.4 

2,364 

.0060 

25 

8.7 

2,363 

.0036 

75 

15.5 

4,505 

.0034 

26 

Disc. 

76 

16.9 

3,636 

.0048 

27 

10.8 

2,474 

.0044 

77 

15.0 

3,109 

.0048 

28 

18.0 

3,010 

.0061 

78 

10.4 

3,088 

.0034 

29 

Disc. 

79 

14.7 

3,284 

.0044 

30 

Disc. 

80 

10.4 

2,993 

.0031 

31 

14.3 

2,495 

.0056 

81 

14.6 

3,313 

.0044 

32 

15.0 

2,527 

.0059 

82 

8.1 

3,137 

.0026 

33 

10.1 

2,469 

.0041 

83 

9.8 

2,834 

.0035 

34 

16.4 

2,599 

.0063 

84 

14.7 

3,604 

.0041 

35 

11.1 

2,036 

.0055 

85 

7.5 

2,609 

.0029 

36 

7.6 

2,188 

.0035 

86 

15.5 

3.254 

.0051 

37 

4.8 

2,292 

.0021 

87 

Disc. 

38 

5.0 

2,315 

.0021 

88 

5.6 

1,886 

.0027 

39 

Disc. 

89 

Disc. 

40 

11.3 

1,838 

.0061 

90 

9.7 

3,241 

.  .0029 

41 

8.6 

2,869 

.0030 

91 

Disc. 

42 

13.2 

2,085 

.0063 

92 

Disc. 

43 

5.0 

1,643 

.0030 

93 

6.8 

2,471 

.0028 

44 

10.1 

2,219 

.0046 

94 

6.0 

1,579 

.0038 

45 

10.0 

2,224 

.0044 

95 

9.9 

2,821 

.0035 

46 

Disc. 

96 

9.7 

1,932 

.0050 

47 

9.6 

1,490 

.0064 

97 

Disc. 

48 

9.4 

1,679 

.0056 

98 

17.1 

3,513 

.0049 

49 

11.8 

2,200 

.0053 

99 

20.7 

3,762 

.0055 

50 

7.7 

1,887 

.0040 

100 

Disc. 

100  THE  PHYTOMETER  METHOD. 

Table  20. — Individual  variability  in  transpiration  of  sunflowers. 


Second  Series. 


No. 

Loss. 

Leaf-area 
(sq.  cm.). 

Loss  per 
leaf-area. 

No. 

Loss. 

Leaf-area 
(sq.  cm.). 

Loss  per 
leaf -area. 

gm. 

gm. 

gm. 

gm. 

1 

19.0 

30.38 

0.65 

60 

24.0 

40.78 

0.58 

2 

20.7 

31.04 

.66 

61 

17.6 

24.26 

.71 

3 

20.8 

30.39 

.68 

62 

15.9 

29.61 

.53 

4 

18.2 

24.42 

.74 

63 

Disc. 

5 

19.6 

33.24 

.58 

64 

Disc. 

6 

18.7 

30.41 

.61 

65 

Disc. 

7 

15.7 

28.75 

.54 

66 

17.3 

23.58 

.73 

8 

17.0 

31.08 

.54 

67 

14.2 

23.85 

.59 

9 

33.7 

52.16 

.64 

68 

20.7 

36.29 

.54 

10 

19.0 

40.84 

.46 

69 

19.9 

36.27 

.52 

11 

16.4 

27.99 

.58 

70 

15.8 

22.59 

.69 

12 

12.4 

26.03 

.51 

71 

13.9 

27.02 

.51 

13 

15.6 

30.74 

.50 

72 

13.6 

25.34 

.53 

14 

18.3 

42.42 

.43 

73 

15.0 

28.99 

.51 

15 

Disc. 

74 

23.6 

39.85 

.59 

16 

6.9 

33 . 50 

.20 

75 

Disc. 

17 

14.5 

36.61 

.31 

76 

10.8 

16.05 

.67 

18 

24.0 

46.55 

.52 

77 

14.8 

23.77 

.62 

19 

19.0 

28.23 

.67 

78 

14.2 

26.92 

.52 

20 

15.9 

26.29 

.60 

79 

14.7 

22.11 

.66 

21 

17.1 

24.06 

.71 

80 

17.3 

34.28 

.54 

22 

27.2 

38.39 

.71 

81 

Disc. 

23 

15.9 

26.58 

.60 

82 

22.1 

37.55 

.59 

24 

14.0 

26.29 

.53 

83 

13.7 

34.52 

.39 

25 

23.5 

33.69 

.70 

84 

23.3 

36.47 

.63 

26 

14.5 

23.59 

.61 

85 

Disc. 

27 

14.2 

28.26 

.50 

86 

20.0 

39.12 

.51 

28 

17.3 

28.67 

.60 

87 

14.9 

29.46 

.50 

29 

15.3 

29.69 

.51 

88 

21.1 

23.85 

.89 

30 

13.2 

23.74 

.55 

89 

11.3 

21.46 

.52 

31 

18.2 

28.64 

.63 

90 

16.3 

28.98 

.56 

32 

29.4 

52.55 

.55 

91 

20.6 

17.95 

.59 

33 

19.7 

26.83 

.73 

92 

Disc. 

34 

27.1 

61.02 

.44 

93 

8.9 

12.18 

.73 

35 

11.0 

24.87 

.44 

94 

22.5 

32.46 

.69 

36 

17.1 

29.04 

.59 

95 

Disc. 

37 

18.4 

35.11 

.52 

96 

21.5 

36.33 

.59 

38 

13.3 

16.92 

.74 

97 

21.6 

41.72 

.51 

39 

12.7 

23.70 

.53 

98 

16.0 

27.12 

.59  • 

40 

16.0 

24.95 

.64 

99 

16.2 

25.10 

.64 

41 

Disc. 

100 

17.9 

23.35 

.76 

42 

33.5 

42.78 

.77 

101 

20.0 

31.44 

.63 

43 

23.9 

40.00 

.59 

102 

Disc. 

44 

17.4 

39.20 

.44 

103 

17.9 

29.41 

.60 

45 

Disc. 

104 

16.2 

29.14 

.55 

46 

17.9 

33.09 

.54 

105 

Disc. 

47 

23.6 

36.63 

.64 

106 

Disc. 

48 

Disc. 

107 

15.0 

22.06 

.67 

49 

14.7 

23.05 

.63 

108 

19.0 

27.48 

.69 

50 

15.8 

24.25 

.65 

109 

21.7 

45.87 

.49 

51 

10.3 

17.61 

.70 

110 

21.5 

34.46 

.62 

52 

17.2 

28.38 

.57 

111 

Disc. 

53 

14.7 

21.28 

.69 

112 

18.9 

30.35 

.62 

54 

14.2 

22.46 

.63 

113 

19.0 

26.13 

.67 

55 

12.4 

23.24 

.53 

114 

Disc. 

56 

13.7 

25.12 

.54 

115 

18.5 

31.43 

.58 

57 

10.7 

22.24 

.48 

116 

Disc. 

58 

9.8 

20.90 

.46 

117 

18.6 

32.61 

.57 

59 

Disc. 

118 

14.7 

22.76 

.69 

TABLES 


101 


Table  21. — Short-period  phytometers,  sun  and  shade,  September  16,  1923. 


Sun. 

Half-shade. 

Shade. 

Loss  in 
weight, 

11  a.  m. 
to  4  p.  m. 

Leaf 

product. 

Loss  per 
leaf  product 
(raised  to 
whole 
numbers). 

Loss  in 
weight, 
11  a.  m. 
to  4  p.  m. 

Leaf 

product. 

Loss  per 
leaf  product 
(raised  to 
whole 
numbers). 

Loss  in 
weight, 
11  a.  m. 
to  4  p.  m. 

Leaf 

product. 

Loss  per 
leafproduct 
(raised  to 
whole 
numbers). 

gm. 

gm. 

gm. 

6.7 

54,171 

123 

1.8 

21,448 

84 

1.1 

25,796 

42 

6.3 

29,484 

213 

1.7 

21,729 

80 

1.1 

19,261 

58 

2.5 

12,511 

200 

1.3 

14,110 

92 

1.1 

22,135 

49 

3.6 

18,946 

190 

1.6 

13,257 

72 

0.4 

13,394 

29 

Average  loss:  Sun,  185;  half-shade,  82;  shade,  44.5;  percentage  of  sun,  100,  44.3,  23.5. 


Table  22. — Short-period  phytometers,  sun  and  shade,  September  18,  1923. 


Station. 


Sun . 

Half-shade . 
Shade . 


9  to  11  a.  m. 

11  a.  m.  to 
lh30m  p.  m. 

lh30m  to 

3  p.  m. 

3  to 

5^30™  p.  m. 

Station. 

Leaf 

product. 

Loss. 

Hourly 
loss  per 
leaf 

product. 

Loss. 

Hourly 
loss  per 
leaf 

product. 

Loss. 

Hourly 
loss  per 
leaf 

product. 

Loss. 

Hourly 
loss  per 
leaf 

product. 

Sun . 

29,484 

gm. 

9.0 

1  177 

gm. 

6.2 

84 

gm. 

3.4 

74 

gm. 

2.5 

33 

Do . 

54,171 

8.2 

75 

9.2 

67 

4.3 

52 

2.4 

17 

Do . 

18,946 

12,511 

21,448 

7.1 

187 

3.1 

65 

2.1 

74 

1.4 

29 

Do . 

5.4 

211 

2.6 

83 

2.1 

111 

.8 

25 

Half -shade . 

3.2 

74 

1.6 

29 

1.2 

37 

.3 

55 

Do . 

14,110 

11,814 

20,692 

19,261 

2.1 

74 

1.9 

53 

.5 

23 

.2 

5 

Do . 

1.2 

50 

1.7 

57 

.3 

16 

.2 

6 

Do . 

1.8 

43 

2.1 

40 

.8 

25 

.3 

5 

Shade . 

1.8 

46 

.9 

18 

.5 

15 

.1 

2 

Do . 

13,394 

25,796 

21,729 

1.1 

41 

.6 

17 

.3 

14 

.1 

2 

Do . 

2.7 

52 

1.8 

27 

.7 

18 

.2 

3 

Do . 

2 

46 

1 

18 

.5 

13 

.2 

3 

Averages: 

Sun . 

167 

75 

78 

26 

Half-shade . 

60 

45 

25 

18 

Sha.de . 

46 

20 

15 

25 

Average  hourly  standard  evaporation. 


9  to  11 
a.  m. 


c.  c. 
1.56 
.71 
.70 


11  a.  m.  to 
lh30“  p.  m. 


c.  c. 
1.39 
.71 
.42 


lh30m  to 
3  p.  m. 


c.  c. 
1.95 
.83 
.46 


3  to 

5h30m  p.  m. 


c.  c. 
1.14 
.33 
.27 


Temperature. 


9  a.  m. 


°  C 
2  39.0 
37.0 
38.5 


11 

a.  m. 


°C. 

15.2 

7.0 

9.2 


2  p.  m. 


°C. 

11.0 

12.0 

10.5 


3h30m 
p.  m. 


°C. 

9.6 

9.3 

9.8 


s^o™ 

p.  m. 


°C. 

4.2 
3.8 

5.3 


1  Raised  to  whole  numbers,  as  in  all  succeeding  tables. 

2  The  9  a.  m.  readings  were  made  at  soil  surface,  all  others  at  3  inches  above  soil  surface  in  shade. 


102 


THE  PHYTOMETER  METHOD 


Table  23. — Short-period  phytometers,  surface  and  angle,  September  20,  1923. 


Position. 

Leaf 

product. 

9  to  11  a.  m. 

11  a.  m.  to 
l^O111  p.  m. 

l^O111  to 
3h30“  p.  m. 

S^O111  to 
4h30m  p.  m. 

Loss. 

Hourly- 
loss  per 
leaf 

product. 

Loss. 

Hourly 
loss  per 
leaf 

product. 

Loss. 

Hourly 
loss  per 
leaf 

product. 

Loss. 

Hourly 
loss  per 
leaf 

product. 

gm. 

gm. 

gm. 

gm. 

Level  turf . 

14,110 

3.7 

131 

6.5 

184 

3.4 

120 

0.6 

28 

Do . 

11,814 

3.3 

148 

3.8 

120 

4.1 

173 

1.1 

62 

Do . 

20,692 

5.1 

120 

6.8 

131 

6.1 

247 

2.4 

77 

Level  gravel . 

12,969 

3.3 

127 

3.6 

111 

2.7 

104 

1.3 

66 

Do . 

12,511 

4.8 

192 

4.6 

147 

4.5 

180 

2.1 

112 

Do . 

18,946 

3.5 

92 

3.5 

74 

2.5 

71 

1.1 

48 

Leaves  horizontal .  . 

21,729 

2.6 

60 

5.2 

96 

3.5 

80 

1 

31 

Do . 

26,028 

5.4 

104 

7.5 

115 

4.7 

90 

1.7 

44 

Do . 

19,261 

5.7 

149 

5.5 

114 

4.5 

117 

1.2 

42 

Leaves  inclined .... 

25,796 

7.3 

142 

9.2 

143 

7.2 

140 

2.9 

75 

Do . 

53,335 

7.9 

74 

11.5 

80 

6.0 

56 

2.5 

31 

Do . 

18,856 

5.7 

151 

8.2 

171 

4.2 

111 

2.2 

78 

Averages : 

Level  turf . 

133 

145 

180 

56 

Level  gravel  .... 

137 

130 

118 

75 

Leaves  horizontal 

104 

108 

96 

39 

Leaves  inclined .  . 

116 

131 

102 

61 

Average  hourly  standard  evaporation. 

Station. 

9  to  11 

a.  m. 

11  a.  m.  to 
1*30“  p.  m. 

l^O®  to 
S^O111  p.  m. 

S^O111  to 
4h30m  p.  m. 

Level  gravel . 

c.  c. 
1.137 

c.  c. 
2.520 

c.  c. 

3.800 

c.  c. 

3.50 

Level  turf . 

1.820 

2.240 

2.970 

1.575 

Sloping  gravel . 

2.307 

3.266 

4.260 

1.657 

Temperature  (°  C.). 

Station. 

llh20m 
a.  m. 

12h45m 
p.  m. 

2h15m 
p.  m. 

3h30m 

p.  m. 

Level  gravel: 

3  in.  above  surface  (shade) . 

19 

22.6 

21.0 

18.0 

Soil  surface . 

32 

38.0 

31.8 

25  8 

Level  turf : 

3  in.  above  surface  (shade) . 

18.6 

21.2 

20.6 

16.0 

Soil  surface . 

18.8 

22.2 

22.6 

20.0 

Gravel  slope: 

3  in.  above  surface  (shade) . 

29.8 

18.2 

Soil  surface . 

45.8 

38.0 

TABLES 


103 


Table  24. — Short-period  phytometers ,  variability,  and  sun  and  shade,  September  21,  1928. 


Station. 


Sun . 

Half-shade . 
Shade . 


Leaf 

product. 

9h40m  to 

1 1^40™  a.  m. 

Station. 

Loss. 

Hourly  loss 
per  leaf 
product. 

Sun . 

14,110 

gm. 

3.8 

135 

Do . 

20,692 

7.5 

181 

Do . 

12,511 

4.8 

112 

Do . 

18,946 

3.6 

95 

Do . 

19,261 

6.9 

178 

Do . 

25,796 

8.5 

165 

Do . 

21,448 

4.6 

107 

Do . 

21,729 

4.6 

106 

Do . 

26,028 

5.1 

98 

Do . 

53,335 

8.6 

81 

Do . 

11,814 

5 

212 

Do . 

12,969 

4.1 

157 

Average,  sun .  . 

135.5 

Average  hourly  standard 
evaporation. 


9h40m  to  11  a.  m. 


c.  c. 
2.64 


llMCP  a.  m.  to 
2h40m  p.  m. 


c.  c. 
2.83 
1.56 
.84 


1 1^40™  a.  m.  to 
2h40m  a.  m. 

Per¬ 
centage 
of  sun. 

Station. 

Loss. 

Hourly  loss 
per  leaf 
product. 

gm. 

S  Sun . 

10.0 

121 

Do . 

5.6 

149 

Do . 

3.4 

89 

Half-shade . 

2.3 

40 

Do . 

5.1 

66 

Do . 

2.2 

34 

Do . 

3.3 

51 

Shade . 

1.2 

15 

j  Do . 

1.7 

11 

Do . 

.4 

11 

Do . 

.3 

7 

Average : 

Sun . 

119.6 

100 

Half-shade. 

47.7 

39 

Shade . 

11.0 

9 

Air-temperature,  in  shade  3  in. 
above  soil  surface  (°  C.). 


12h50m  p.  m. 


20.8 

18.2 

12 


3  p.  m. 


1  17 
17 

13.8 


1  21.8°  in  sun. 


104 


THE  PHYTOMETER  METHOD 


Table  25. — Short-period  phytometers ,  slope-exposure,  September  26-27 ,  1923. 


8h30m  to 
llh30m  a.  m. 

llh45m  a.  m.  to 
3  p.  m. 

3  to  6  p.  m. 

6  p.  m.  to 
6h45m  a.  m. 

Station. 

Leaf 

product. 

Loss. 

Hourly 
loss  per 
leaf 

product. 

Loss. 

Hourly 
loss  per 
leaf 

product. 

Loss. 

Hourly 
loss  per 
leaf 

product. 

Loss. 

Hourly 
loss  per 
leaf 

product. 

South . 

34,688 

23,747 

gm. 

10.8 

104 

gm. 

8.1 

72 

gm. 

1.7 

16 

gm. 

0.8 

2 

Do . 

8 

112 

5.3 

66 

1 

14 

1.1 

3 

Do . 

36,627 

13.1 

119 

10.1 

85 

1.9 

17 

.5 

1 

North . 

35,175 

12.2 

116 

15.5 

136 

3.8 

36 

3.5 

7 

Do . 

27,616 

44,779 

9.7 

105 

10.1 

113 

3.6 

43 

2.3 

6 

Do . 

12.2 

90 

x9.8 

76 

4.8 

40 

1.8 

3 

Average : 

South . 

112 

108 

40 

5 

North . 

104 

74 

16 

2 

Average  standard 
hourly  evapora¬ 
tion: 

South . 

c.  c. 
2.75 

c.  c. 

3.64 

c.  c. 

3.25 

c.  c. 

2.05 

North . 

1.60 

3.01 

2.52 

1.32 

Temperature,  °  C. 


Stations. 


8h40m 
a.  m. 

lO^O"1 
a.  m. 

12  m. 

3  p.  m. 

6  p.  m. 

e^o™ 

a.  m. 

20.4 

22.2 

25.1 

21.8 

13.6 

6.4 

11.4 

18.6 

19.8 

21.3 

13.4 

6.2 

South , 
North 


BIBLIOGRAPHY. 

Baker,  F.  S.  1916.  Aspen  as  a  temporary  forest  type.  Jour.  For.,  16:294. 

Briggs,  L.  J.,  and  H.  L.  Shantz.  1912.  The  wilting  coefficient  for  different  plants  and 
its  indirect  determination.  Bur.  Plant.  Ind.  Bull.  230. 

-  - .  1913.  The  water  requirement  of  plants.  Bur.  Plant.  Ind.  Bull.  284. 

Clements,  E.  S.  1905.  The  relation  of  leaf  structure  to  physical  factors.  Trans.  Am. 
Mic.  Soc.,  26:  19. 

Clements,  F.  E.  1904.  Development  and  structure  of  vegetation.  Rep.  Bot.  Surv. 
Nebr.,  7. 

- .  1905.  Research  methods  in  ecology. 

- .  1907.  Causes  of  alpine  dwarfing.  Science,  25 :  287. 

• - .  1907a.  Plant  physiology  and  ecology. 

- .  1916.  Plant  succession.  Carnegie  Inst.  Wash.  Pub.  No.  242. 

- .  1920.  Plant  indicators.  Carnegie  Inst.  Wash.  Pub.  No.  290. 

- .  1921.  Aeration  and  air-content.  Carnegie  Inst.  Wash.  Pub.  No.  315. 

- and  G.  W.  Goldsmith.  1919-1922.  The  phytometer  method.  Carnegie  Inst. 

Wash.  Year  Books  18-21. 

- ,  - .  1923.  The  phytometer  method.  Carnegie  Inst.  Wash.  Year  Book 

22:303. 

-  and  H.  M.  Hall.  1918.  Reciprocal  transplants.  Carnegie  Inst.  Wash.  Year 

Book  17:  292. 

- ,  - .  1919-1923.  Experimental  taxonomy.  Carnegie  Inst.  Wash.  Year 

Books  18-21. 

- -  and  J.  V.  G.  Loftfield.  1923.  Permanent  quadrats  and  transects.  Carnegie 

Inst.  Wash.  Year  Book  22:  320. 

-  and  D.  C.  Lutjeharms.  1921-1922.  Slope-exposure  studies.  Carnegie  Inst. 

Wash.  Year  Book  20-21. 

— -  and  J.  E.  Weaver.  1918.  The  phytometer  method.  Carnegie  Inst.  Wash. 

Year  Book  17:  288. 

- ,  - .  1924.  Experimental  vegetation.  Carnegie  Inst.  Wash.  Pub.  No.  355. 

Crump,  W.  B.  1913.  The  coefficient  of  humidity:  A  new  method  of  expressing  the 
soil  moisture.  New  Phyt.,  12:  125. 

Gain,  E.  1895.  Action  de  l’eau  du  sol  sur  la  vegetation.  Rev.  Gen.  Bot.,  7 :  15. 
Hedgcock,  G.  G.  1902.  The  relation  of  the  water-content  of  the  soil  to  certain  plants, 
principally  mesophytes.  Rep.  Bot.  Surv.  Nebr.,  6. 

Heinrich,  H.  1874.  Ueber  das  Vermogen  der  Pflanzen  den  Boden  an  Wasser  zu 
erschopfen.  Tagb.  Naturf.  Breslau,  1874. 

Hesselmann,  H.  1904.  Zur  Kenntnis  des  Pflanzenlebens  schwedischer  Laubwiesens. 
Mitt.  Bot.  Inst.  Univ.  Stockholm. 

Hildebrandt,  F.  M.  1921.  A  physiological  study  of  the  climatic  conditions  of  Mary¬ 
land,  as  measured  by  plant  growth.  Physiol.  Res.,  2:  341.  , 

Hole,  R.  S.  1921.  The  regeneration  of  sal  ( Shorea  robusta )  forests.  A  study  in 
economic  oecology.  Indian  For.  Rec.,  8:  163. 

- and  P.  Singh.  1916.  Oecology  of  sal  ( Shorea  robusta )  forests.  A  study  in  eco¬ 
nomic  oecology.  Indian  For.  Rec.,  8:  163. 

Iljin,  W.  S.  1916.  Relation  of  transpiration  to  assimilation  in  steppe  plants.  Jour. 
Ecol.,  4:  65. 

Jean,  F.  C.,  and  J.  E.  Weaver.  1923.  Relation  of  holard  to  root  development  and 
yield.  Carnegie  Inst.  Wash.  Year  Book  22:313. 

-  - .  1924.  Root  behavior  and  crop  yield  under  irrigation.  Carnegie  Inst. 

Wash.  Pub.  No.  357. 

Johnson,  E.  S.  1921.  The  seasonal  march  of  the  climatic  conditions  of  a  greenhouse, 
as  related  to  plant  growth.  Md.  Agr.  Expt.  Sta.  Bull.  245;  Mon. 
Weather  Rev.  50:  197,  1922. 

Livingston,  B.  E.,  and  F.  T.  McLean.  1916.  A  living  climatological  instrument. 
Science,  43:  362. 

Lutjeharms,  D.  C.  1924.  Environmental  differences  on  north  and  south  slopes  of  a 
canyon,  based  upon  measurements  of  climatic  factors  and  plant  growth. 

105 


106 


THE  PHYTOMETER  METHOD. 


McLean,  F.  T.  1917.  A  preliminary  study  of  climatic  conditions  in  Maryland,  as 
related  to  plant  growth.  Physiol.  Res.,  2 :  129. 

McLean,  R.  C.  1919.  Studies  in  the  ecology  of  tropical  rain-forest,  with  special 
reference  to  the  forests  of  south  Brazil.  Jour.  Ecol.,  7 :  5. 

Ridgway,  C.  S.  1918.  A  promising  chemical  photometer  for  plant  physiological 
research.  Plant  World,  21:  234;  Mon.  Weather  Rev.,  46:  117. 

Sampson,  A.  W.  1919.  Climate  and  plant  growth  in  certain  vegetative  associations. 
U.  S.  Dept.  Agr.  Bull.  700. 

— - and  L.  M.  Allen.  1909.  Influence  of  physical  factors  on  transpiration.  Minn. 

Bot.  Studies,  4:  33. 

Sachs,  J.  1859.  Ueber  den  Einfluss  der  chemischen  und  der  physikalischen  Beschaffen- 
heit  des  Bodens  auf  die  Transpiration.  Landw.  Vers.  Stat.  1. 

Taylor,  W.  P.,  and  J.  V.  G.  Loftfield.  1922-23.  Destruction  of  the  range  by  prairie- 
dogs.  Carnegie  Inst.  Wash.  Year  Book  21:  353;  22:314. 

Weaver,  J.  E.  1924.  Plant  production  as  a  measure  of  environment.  Jour.  Ecol. 
12:205;  cf.  Carnegie  Inst.  Wash.  Year  Books  20:400,  22:312. 

-  and  J.  W.  Crist.  1924.  Direct  measurement  of  water-loss  from  vegetation 

without  disturbing  the  normal  structure  of  the  soil.  Ecology  5:153. 

- ,  F.  C.  Jean,  and  J.  W.  Crist.  1922.  Development  and  activities  of  roots  of 

crop  plants.  Carnegie  Inst.  Wash.  Pub.  No.  316. 

- and  A.  F.  Thiel.  1917.  Ecological  studies  in  the  tension  zone  between  grass¬ 
land  and  woodland.  Rep,  Bot.  Surv.  Nebr.,  n.  s.,  1. 


CLEMENTS  AND  GOLDSMITH 


PLATE  2 


A.  Mixed  prairie  at  plains  station,  6,100  feet,  Colorado  Springs. 

B.  Montane  forest  ( Pseudotsuga  mucronata )  at  montane  station,  8,600  feet,  Alpine 

Laboratory. 


CLEMENTS  AND  GOLDSMITH 


PLATE  3 


A.  Subalpine  forest  ( Picea  engelmanni )  at  subalpine  station,  10,800 

feet,  Pike’s  Peak. 

B.  Battery  of  large  wheat  phytometers,  montane  station,  1920. 


CLEMENTS  AND  GOLDSMITH 


PLATE  4 


A.  Battery  of  sunflower  phytometers,  plains  station,  1918. 

B.  Battery  of  sunflower  phytometers,  montane  station,  1918. 

C.  Battery  of  oat  and  wheat  phytometers,  montane  station,  1918. 


CLEMENTS  AND  GOLDSMITH 


PLATE  5 


•  ■  -  7  ’ 


B.  Half-shade  station,  1923 


A.  Sun  station,  1923 


CLEMENTS  AND  GOLDSMITH 


PLATE  6 


A.  Full-shade  station,  1923. 

B.  Photosynthesis  and  respiration  phytometers,  sun  station,  1923. 


CLEMENTS  AND  GOLDSMITH 


PLATE  7 


A.  Sunflower  phytometers,  sun  station,  first  series,  1923. 

B.  Same,  half-shade  station. 

C.  Same,  full-shade  station. 


CLEMENTS  AND  GOLDSMITH 


PLATE  8 


11  11  1 

-&44I  Jif  m 

ill  jl 

L,.  i 

1  Jii  m  /fl 

#  M  fpl  a  !J| 

l#A\  j§g§g§||f 

Wmm  mbseM  fm 

ABk..  flSSBS 

17 


33 


A.  Growth  of  shoots,  shade,  half-shade,  and  sun  stations,  second  series,  1923. 

B.  Growth  of  roots,  sun,  half-shade,  and  shade  stations. 


CLEMENTS  AND  GOLDSMITH 


PLATE  9 


A.  Battery  of  sunflower  phytometers,  slope-exposure  transect,  mesocline 

station. 

B.  Same,  canyon-bottom  station. 

C.  Same,  xerocline  station. 


- 


CLEMENTS  AND  GOLDSMITH 


PLATE  10 


A.  Sod-core  phytometers  and  details  of  installation,  Burlington.  Colorado. 

B.  Clip-quadrat  phytometer  in  Bulbilis-Bouteloua  short-grass,  Burlington. 


CLEMENTS  AND  GOLDSMITH 


PLATE  11 


Total  Protection  Prairie  Dog 


plot 


Cattle  Grazed 

PLOT 


A.  Agropyrum  glaucum  from  clip-quadrats  in  cattle-prairiedog  inclosure,  cattle 

exclosure,  and  open  range,  Grand  Canyon,  Arizona. 

B.  Cattle-rodent  exclosure.  Santa  Rita  Range  Reserve.  Tucson,  Arizona,  showing 

growth  of  desert-plains  grassland  under  complete  protection. 


DEPARTMENT  0>  :'lk-  ' 

_  r  r  •  i  ,  ,K  UW»* 

Y,  STATE  COILT-G'  • 

,-r  ii  it.  M  T  . 


..  n  l  i  i  h  w  i  f  <ii 


